Regimens of tafenoquine for prevention of malaria in malaria-naive subjects

ABSTRACT

Methods of prevention of symptomatic malaria in a malaria-naïve, G6PD-normal human subject comprising administering to the human subject a compound of Formula (I), a pharmaceutically acceptable salt thereof, or pharmaceutical composition comprising a compound of Formula (I). A compound of Formula (I) can be administered prior to potential exposure of a species of  Plasmodium , during potential exposure of a species of  Plasmodium , and after potential exposure of a species of  Plasmodium . The methods of the invention also pertains to kits comprising specific doses of Formula (I), a pharmaceutically acceptable salt thereof, or pharmaceutical composition comprising a compound of Formula (I), and instructions for administration of dosing quantity and frequency. The methods of the invention also pertain to determining doses of Formula (I) that meet the general regulatory requirement for a drug to be efficacious in the prevention of malaria in malaria-naïve subjects. The methods of the invention further pertain to using the described algorithm to derive dosing regimens which can provide protection against symptomatic malaria in malaria-naïve, G6PD-normal subjects.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application pursuant to 35U.S.C. § 371 of International Patent Application PCT/US2015/063425,filed on Dec. 2, 2015, and published as WO 2016/089995 on Jun. 9, 2016,which claims priority to U.S. Provisional Patent Application 62/086,355,filed on Dec. 2, 2014, all of which are incorporated herein by referencein their entireties for all purposes.

BACKGROUND OF THE INVENTION

There are 217,000,000 cases of malaria and 627,000 deaths annually intropical countries (http://www.who.int/gho/malaria/epidemic/en/). Thedisease is caused by five species of Plasmodium: P. vivax, P.falciparum, P. ovale, P. knowlsi, and P. malariae, all protozoanparasites transmitted by mosquitoes. The symptoms of malaria are causedby the amplification of the parasite in red blood cells, after aninitial cycle of replication in the liver. Individuals who reside inareas of heavy malaria transmission develop a partial immunity to thedisease after repeated exposure to the parasites which prevents thedevelopment of symptoms in response to new infection. Travelers fromtemperate countries, who have not been exposed to malaria, are termed‘non-immune individuals’ or ‘marlaria-naïve,’ are at high risk of severeclinical disease and death if they contract malaria during a visit to atropical country. These individuals, to prevent malaria, are oftenadministered a course of ‘prophylactic’ antimalarial drugs (e.g.,mefloquine, chloroquine, doxycycline, primaquine, oratovaquone-proguanil) that maintain a minimum protective level of activedrug in their blood during travel. Upon return, these individuals musttake a 14-day course of primaquine to kill the latent stages of P. vivaxand P. ovale and/or continue to maintain active blood levels of drug tosuppress any remaining viable blood stage parasites of all species.

An appropriate prophylactic antimalarial drug, dosed in a manner tomaintain therapeutic levels indefinitely, could protect a non-immuneindividual from contracting symptomatic malaria, caused by any humanspecies of Plasmodia, during the period of exposure to malaria vectorsif it killed (i) 100% of developing liver schizonts upon entry into theliver after a mosquito bite, or (ii) 100% of merozoites upon their entryfrom the liver into the blood stream. In the special case of relapsingmalaria parasites such as P. vivax and P. ovale, a hypothetical malariadrug would have to exhibit any of the aforementioned inhibitoryproperties, plus, in addition, kill developing liver schizonts after theactivation of latent hypnozoites. However, in order to maintain highlevels of clinical protective efficacy, 100% killing of merozoitesemerging from the liver is an absolute requirement if a drug does notkill 100% of developing liver schizonts (originating from eithersporozoites or hypnozoites).

Tafenoquine is an 8-aminoquinoline analog of primaquine, the approveddrug that is primarily used to eliminate the latent liver stages of P.vivax (Shanks and Edstein 2005). Tafenoquine is known to exhibit apotent inhibitory effect on developing liver schizonts. Tafenoquine isgenerally presumed to also exhibit antihypnocytocidal effects against P.vivax. The inhibitory effect of tafenoquine on asexual blood stageparasites is also known. The drug is active against the blood stages ofP. falciparum in vitro, P. berghei in mice in vivo, and cured bothchloroquine sensitive and resistant P. vivax infections in Aotusmonkeys. Tafenoquine is being developed for the complete, also known asradical, cure of P. vivax malaria, and for the chemoprophylaxis (i.e.,prevention) of malaria in malaria-naïve travelers. Structural featuresinstalled to block metabolic sites on the core 8-aminoquinoline scaffoldprovide the drug with an extremely long half-life (weeks) relative toprimaquine (hours). Tafenoquine's long half-life makes it suitable forweekly administration, making it an ideal replacement for other weeklydrugs such as chloroquine (limited efficacy due to resistance) andmefloquine (no longer commonly prescribed due to its association withadverse neurologic effects). The capacity for weekly administration(better compliance) and utility against the dormant, hypnozoites of P.vivax (14-day treatment with primaquine not required) confer superiorutility to tafenoquine relative to daily prophylactic drugs such asdoxycycline and atovaquone-proguanil.

Glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency) ischaracterized by abnormally low levels of G6PD, due to an X-linkedrecessive genetic deficiency and is the most common human enzyme defect.G6PD is a metabolic enzyme involved in the pentose phosphate pathway andis especially important in red blood cell metabolism (Frank 2005).G6PD-deficient individuals may exhibit hemolytic anemia in response to anumber of causes, most commonly infection or exposure to certainmedications or fava beans. Individuals that are carriers of the G6PDallele appear to be protected to some extent against malaria. Further,in some cases dominant males have shown complete immunity to thedisease. This accounts for the persistence of the allele in certainpopulations in that it confers a selective evolutionary survivaladvantage (Lewis, Ricki).

Many substances are potentially harmful to people with G6PD deficiency.Variation in response to these substances makes individual predictionsdifficult. Such harmful substances include antimalarial drugs which cancause acute hemolysis in people with G6PD deficiency. These drugsinclude primaquine, pamaquine, and chloroquine. There is evidence thatother antimalarials may also exacerbate G6PD deficiency, but only athigher doses. Sulfonamides (such as sulfanilamide, sulfamethoxazole, andmafenide), thiazolesulfone, methylene blue, and naphthalene should alsobe avoided by people with G6PD deficiency as they antagonize folatesynthesis, as should certain analgesics (such as aspirin,phenazopyridine, and acetanilide) and several non-sulfa antibiotics(nalidixic acid, nitrofurantoin, isoniazid, dapsone, and furazolidone)(Frank J E; Warrel, David A.; and Beutler, E.). Henna has been known tocause haemolytic crisis in G6PD-deficient infants (Raupp P, et al.).

Tafenoquine, like other 8-aminoquinolines, may cause hemolytic anemia inindividuals with G6PD deficiency; such anemia is dose-related. For thisreason, tafenoquine can be more readily given to individuals shown tohave normal levels of G6PD in their blood. Although in theory this canbe accomplished through the use of one of at least 30 commercial testkits available, the gold standard for the diagnosis of G6PD deficiencyis to use a direct, quantitative enzymatic assay to establish the amountof G6PD in the blood (von Seidlein, et al.). This test is usuallyadministered as a screening test prior to travel or deployment by traveldoctors, public health or military medical personnel, as a routinecomponent of a pre-travel check list. Best practice is to perform doublescreening to reduce the likelihood of false negative results.

None of the prior regimens of tafenoquine described in the literatureprovide the optimal balance between tolerability and achieving asufficiently high steady state minimum concentration of tafenoquineabove a threshold of therapeutic efficacy to prevent symptomatic malariain malaria-naïve, normal Glucose-6-phosphate dehydrogenase (G6PD)individuals. The present invention satisfies this long-felt need byspecifying a set of dosing regimens which achieve the minimumconcentration required to achieve protection from development ofsymptomatic malaria in malaria-naïve individuals while minimizingadverse events.

Furthermore, the present invention specifies dosing regimens in whichthe overall exposure to tafenoquine may not change, but the maximumsteady state concentrations will be reduced, and the minimum steadystate concentrations will be increased to ensure therapeutic efficacy bymore frequent tafenoquine dosing.

Further, there are no available antimalarial drugs that work everywherein the world, can be administered once weekly, and have activity againstthe latent liver stages of P. vivax. The Applicants' invention directlyaddresses all of these therapeutic needs and also does so with onedrug—tafenoquine.

Post-exposure prophylaxis is currently achieved using a combination ofdaily primaquine plus a blood schizonticidal drug like doxycycline ormefloquine. Tafenoquine fulfills all these tasks in monotherapy dosesadministered once daily to once weekly following a potential exposure toa Plasmodium species. In some aspects, tafenoquine can providepost-exposure prophylactic protection by relying on higher dosing duringpotential exposure and the relatively long half-life of the drug toensure protective levels of tafenoquine are maintained for at leastthree weeks after returning from a malarious area.

SUMMARY OF THE INVENTION

The present invention pertains to novel dosing regimens for tafenoquinefor malaria prophylaxis. In some embodiments, the regimens areadministered to malaria-naïve subjects. In other embodiments, thesubjects are Glucose-6-phosphate dehydrogenase (G6PD) normal humansubjects. The present invention pertains to prophylaxis andpost-exposure prophylaxis against malaria of all species. The presentinvention also pertains to methods for determining doses of tafenoquinethat meet the Food and Drugs Administration (FDA) and other non US-basedregulatory authorities' general regulatory requirement for a malariaprophylactic drug to be 95% effective in the prevention of symptomaticmalaria in malaria-naïve, Glucose-6-phosphate dehydrogenase (G6PD)normal human subjects. The present invention describes dosing regimenswhich can provide protection against symptomatic malaria under variousscenarios in groups of people within certain age range and body weightranges.

In one aspect, the method of prevention of malaria in a human subjectcomprises administering to the human subject an initial dose of acompound of Formula (I), a pharmaceutically acceptable salt thereof, ora pharmaceutical composition comprising a compound of Formula (I),wherein said initial dose comprises one or more doses, e.g., at leastonce per day for three days, prior to potential exposure of at least onespecies of Plasmodium; followed by administering to the human subject anexposure dose of a compound of Formula (I), a pharmaceuticallyacceptable salt thereof, or a pharmaceutical composition comprising acompound of Formula (I), one or more times per week, during potentialexposure of at least one species of Plasmodium, e.g., once per day, onceevery two to six days, or once per week; followed by administering tothe human subject a post-exposure dose of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), one or more times, forexample at least once per day for three days, once per week for threeweeks, or at least three times, after potential exposure of at least onespecies of Plasmodium, and, wherein a serum or plasma concentration ofat least 80 ng/mL of a compound of Formula (I) is attained prior topotential exposure, maintained during potential exposure, and maintainedfor at least three weeks after potential exposure to at least onespecies of Plasmodium, and wherein the human subject is malaria-naïveand Glucose-6-phosphate dehydrogenase (G6PD) normal, and wherein Formula(I) has the following structure,

An alternative name for the compound of Formula (I) is[2,6-Dimethoxy-4-methyl-5-[3-(trifluoromethyl)phenoxy]quinolin-8-yl]pentane-1,4-diamine,or a pharmaceutical acceptable salt thereof. Formula (I) may also havethe following related structure,

The chemical Abstract Service (CAS) number for above identifiedsuccinate salt structure is 106635-81-8.

In another aspect, the present invention pertains to a method ofprevention of post-exposure malaria in a human subject, comprisingadministering to the human subject a primary dose of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I); andadministering to the human subject a post-exposure dose of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I), afteradministration of said primary dose and after potential exposure to atleast one species of Plasmodium, wherein said primary dose comprises oneor more individual doses sufficient to achieve a serum or plasmaconcentration of at least about 80 ng/mL of a compound of Formula (I),and wherein said post-exposure dose comprises one or more individualdoses sufficient to maintain for at least three weeks after potentialexposure of at least one species of Plasmodium, a serum or plasmaconcentration of at least about 80 ng/mL of a compound of Formula (I),wherein the human subject is malaria-naïve and G6PD normal, and whereinFormula (I) has the following structure,

In another aspect, the invention pertains to a method of prevention ofmalaria in a human subject, comprising administering to the humansubject an initial dose of a compound of Formula (I), a pharmaceuticallyacceptable salt thereof, or a pharmaceutical composition comprising acompound of Formula (I), one or more times prior to potential exposureof at least one species of Plasmodium, wherein each said initial dose isbetween about 75 and about 299 mg; and administering to the humansubject an exposure dose of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), one or more times perweek during potential exposure of at least one species of Plasmodium,wherein the total administered amount of the exposure dose is betweenabout 175 and 195 mg per week, and wherein the human subject ismalaria-naïve and G6PD normal, and wherein Formula (I) has the followingstructure,

The invention also pertains to kits for carrying out the methodsdescribed herein. In one specific embodiment, the kit comprises one ormore initial dose(s) of about 40 to about 299 mg of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I);multiple exposure doses wherein the total administered amount ofexposure dose is about 75 to about 299 mg per week of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I); one ormore post-exposure dose(s) of about 40 to about 299 mg of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I); andinstructions for taking said initial dose(s) one or more times prior topotential exposure of at least one species of Plasmodium, and takingsaid exposure dose one or more times per week, for example once per day,once every two to six days, or once per week, during potential exposureof at least one species of Plasmodium, and for taking said post-exposuredose(s) one or more times after potential exposure of at least onespecies of Plasmodium, and wherein Formula (I) has the followingstructure,

In another embodiment, the invention pertains to a kit comprising one ormore initial doses of a compound of Formula (I), a pharmaceuticallyacceptable salt thereof, or a pharmaceutical composition comprising acompound of Formula (I), wherein the total combined amount of thecompound of Formula (I) in all pre-exposure doses exceeds about 500 mg;and a plurality of exposure doses of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), wherein the totalweekly amount of the compound of Formula (I) is at least about 175 mgper week; and instructions for taking said initial dose(s) one or moretimes prior to potential exposure of at least one species of Plasmodium,and taking said exposure dose two or more times per week, whereinFormula (I) has the following structure,

The invention also pertains to a kit comprising one or more primarydose(s) of about 40 to about 299 mg of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I); one or morepost-exposure dose(s) of about 40 to about 299 mg of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I); andinstructions for taking said primary dose(s) one or more times prior totaking said post-exposure dose(s) one or more times, for example atleast once per day for three days, once per week for one to three weeks,three times, or at least three times after potential exposure of atleast one species of Plasmodium, and wherein Formula (I) has thefollowing structure,

In one aspect, the method of prevention of malaria in a human subjectcomprises administering to the human subject one or more initial dose(s)(e.g., at least once per day for three days, once per week for one tothree weeks, three times, or at least three times) prior to potentialexposure of at least one species of Plasmodium, wherein each saidinitial dose is about 40 to about 399 mg; followed by administration ofone or more exposure dose(s) of a compound or Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), from about once perday to about once per week during potential exposure of at least onespecies of Plasmodium, wherein the total administered amount of theexposure dose is about 75 to about 399 mg per week, followed byadministration of one or more post-exposure dose(s) of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I), (e.g.,one or more times, at least once per day for three days, once per weekfor three weeks, three times, or at least three times) after potentialexposure of at least one species of Plasmodium; wherein each saidpost-exposure dose is about 40 to about 399 mg, and wherein the humansubject is malaria-naïve and G6PD normal. In certain embodiments, theinitial dose(s) is administered to achieve prior to potential exposure,the exposure doses are administered to maintain during potentialexposure, and the post-exposure dose(s) is administered to maintain forat least three weeks after potential exposure, a serum or plasmaconcentration of a compound of Formula (I) or tafenoquine of betweenabout 50 ng/mL and about 400 ng/mL in the subject. In other embodiments,the serum or plasma concentration achieved in the subject is at leastabout 50 ng/mL, 80 ng/mL, 100 ng/mL, 125 ng/mL, 150 ng/mL, or 175 ng/mLof tafenoquine or a compound of Formula (I). In certain aspects, theserum or plasma concentration is measured as the median Cmin of apopulation of subjects administered the given dose of a compound ofFormula (I). In other aspects, the serum or plasma concentration ismeasured as the 5^(th) percentile Cmin of a population of subjectsadministered the given dose of a compound of Formula (I). In furtheraspects, the serum or plasma concentration of a compound of Formula (I),or tafenoquine is measured in the individual subject.

In another aspect of the invention, the method of prevention of malariain a human subject is a method of prevention of post-exposure malariaand comprises administering to the human subject one or more primarydose(s) of a compound of Formula (I), a pharmaceutically acceptable saltthereof, or a pharmaceutical composition comprising a compound ofFormula (I), one or more times, for example at least once per day forthree days, once per week for one to three weeks, or three times,wherein each said primary dose is about 40 to about 399 mg; followed byadministering to the human subject a post-exposure dose of a compound ofFormula (I), a pharmaceutically acceptable salt thereof, or apharmaceutical composition comprising a compound of Formula (I), one ormore times after potential exposure; wherein each said post-exposuredose is about 40 to about 399 mg, and wherein the human subject ismalaria-naïve and G6PD normal. In certain embodiments, the primarydose(s) is administered to achieve, and the post-exposure dose(s) isadministered to maintain for at least three weeks after potentialexposure, a serum or plasma concentration of a compound of Formula (I)or tafenoquine of between about 50 ng/mL and about 400 ng/mL in thesubject. In other embodiments, the serum or plasma concentrationachieved in the subject is at least about 50 ng/mL, 80 ng/mL, 100 ng/mL,125 ng/mL, 150 ng/mL, or 175 ng/mL of tafenoquine or a compound ofFormula (I). In certain aspects, the serum or plasma concentration ismeasured as the median Cmin of a population of subjects administered thegiven dose of a compound of Formula (I). In other aspects, the serum orplasma concentration is measured as the 5^(th) percentile Cmin of apopulation of subjects administered the given dose of a compound ofFormula (I). In further aspects, the serum or plasma concentration of acompound of Formula (I), or tafenoquine is measure in the individualsubject.

In one embodiment, the initial doses are administered at intervals ofabout once per day. In further embodiments, the initial doses areadministered at intervals of about once every two to six days. In yetother embodiments, the initial doses are administered at intervals ofabout every two days. In another embodiment, the initial doses areadministered at intervals of about every three days. In yet otherembodiments, the initial doses are administered at intervals of aboutevery four days. In further embodiments, the initial doses areadministered at intervals of about every five days. In still anotherembodiment, the initial doses are administered at intervals of aboutevery six day. In other embodiments, the initial doses are administeredat intervals of about once per week. In further embodiments, the initialdoses are administered at least three times. In other embodiments, theinitial doses are administered for about one week, about two weeks, orabout three weeks. In yet other embodiments, the initial doses aredivided doses that are administered about two to about four times perday. In other embodiments, the initial doses are divided doses that areadministered about two, three, or four times per day.

In certain embodiments, the initial doses are administered for about1-21 days. In other embodiments, the initial doses are administered forabout 1-14 days, 1-10 days, 1-7 days, 1-5 days, or 1-3 days. In yetother embodiments, the initial doses are administered for about 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21days.

In one embodiment, the exposure doses are administered at intervals ofabout once per day. In further embodiments, the exposure doses areadministered at intervals of about once every two to six days. Infurther embodiments, the exposure doses are administered at intervals ofabout every two days. In another embodiment, the exposure doses areadministered at intervals of about every three days. In yet otherembodiments, the exposure doses are administered at intervals of aboutevery four days. In further embodiments, the exposure doses areadministered at intervals of about every five days. In anotherembodiment, the exposure doses are administered about every six days. Inother embodiments, the exposure doses are administered at intervals ofabout once per week. In further embodiments, the exposure doses aredivided doses that are administered about two to about four times perday. In yet other embodiments, the exposure doses are divided doses thatare administered about 2, 3, or 4 times per day.

In certain embodiments of the invention, the initial dose, the exposuredose, the primary dose, and/or the post-exposure dose is about 10 toabout 399 mg and is administered at various frequencies per week fromonce every day up to once every seven days, wherein the total amount ofexposure dose administered in a week is about 75 to about 399 mg. Infurther embodiments, the initial dose, the exposure dose, the primarydose, and/or the post-exposure dose is about 10 to about 57 mg and isadministered about once per day. In some embodiments, the initial dose,the exposure dose, the primary dose, and/or the post-exposure dose isabout 15, about 20, about 25, about 30, about 35, about 40, about 45,about 50, or about 55 mg and is administered once per day. In stillother embodiments, the initial dose, the primary dose, and/or thepost-exposure dose is about 57 to about 399 mg and is administered aboutonce per day. In further embodiments, the initial dose, the primarydose, and/or the post-exposure dose is about 60, about 65, about 70,about 75, about 80, about 85, about 90, about 95, about 100, about 105,about 110, about 115, about 120, about 125, about 130, about 135, about140, about 145, about 150, about 155, about 160, about 165, about 170,about 175, about 180, about 185, about 190, about 200, about 205, about210, about 215, about 220, about 225, about 230, about 235, about 240,about 245, about 250, about 255, about 260, about 265, about 270, about275, about 280, about 285, about 290, about 295, about 300, about 305,about 310, about 315, about 320, about 325, about 330, about 335, about340, about 345, about 350, about 355, about 360, about 365, about 370,about 375, about 380, about 385, about 390, or about 395 mg and isadministered once per day. In yet other embodiments, the initial dose,the exposure dose, the primary dose, and/or the post-exposure dose isabout 21 to about 114 mg and is administered about once every two days.In some embodiments, the initial dose, the exposure dose, the primarydose, and/or the post-exposure dose is about 25, about 30, about 35,about 40, about 45, about 50, about 55, about 60, about 65, about 70,about 75, about 80, about 85, about 90, about 95, about 100, about 105,or about 110 mg and is administered about once every two days. In stillother embodiments, the initial dose, the primary dose, and/or thepost-exposure dose is about 114 to about 399 mg and is administeredabout once every two days. In still other embodiments, the initial dose,the primary dose, and/or the post-exposure dose is about 115, about 120,about 125, about 130, about 135, about 140, about 145, about 150, about155, about 160, about 165, about 170, about 175, about 180, about 185,about 190, about 200, about 205, about 210, about 215, about 220, about225, about 230, about 235, about 240, about 245, about 250, about 255,about 260, about 265, about 270, about 275, about 280, about 285, about290, about 295, about 300, about 305, about 310, about 315, about 320,about 325, about 330, about 335, about 340, about 345, about 350, about355, about 360, about 365, about 370, about 375, about 380, about 385,about 390, or about 395 mg and is administered every two days. Infurther embodiments, the initial dose, the exposure dose, the primarydose, and/or the post-exposure dose is about 32 to about 171 mg and isadministered about once every three days. In some embodiments, theinitial dose, the exposure dose, the primary dose, and/or thepost-exposure dose is about 35, about 40, about 45, about 50, about 55,about 60, about 65, about 70, about 75, about 80, about 85, about 90,about 95, about 100, about 105, about 110, about 115, about 120, about125, about 130, about 135, about 140, about 145, about 150, about 155,about 160, about 165, or about 170 mg and is administered about onceevery three days. In still other embodiments, the initial dose, theprimary dose, and/or the post-exposure dose is about 171 to about 399 mgand is administered about once every three days. In further embodiments,the initial dose, the primary dose, and/or the post-exposure dose isabout 175, about 180, about 185, about 190, about 200, about 205, about210, about 215, about 220, about 225, about 230, about 235, about 240,about 245, about 250, about 255, about 260, about 265, about 270, about275, about 280, about 285, about 290, about 295, about 300, about 305,about 310, about 315, about 320, about 325, about 330, about 335, about340, about 345, about 350, about 355, about 360, about 365, about 370,about 375, about 380, about 385, about 390, or about 395 mg and isadministered once every three days. In yet other embodiments, theinitial dose, the exposure dose, the primary dose, and/or thepost-exposure dose is about 42 to about 230 mg and is administered aboutonce every four days. In some embodiments, the initial dose, theexposure dose, the primary dose, and/or the post-exposure dose is about45, about 50, about 55, about 60, about 65, about 70, about 75, about80, about 85, about 90, about 95, about 100, about 105, about 110, about115, about 120, about 125, about 130, about 135, about 140, about 145,about 150, about 155, about 160, about 165, about 170, about 175, about180, about 185, about 190, about 200, about 205, about 210, about 215,about 220, or about 225 mg and is administered about once every fourdays. In still other embodiments, the initial dose, the primary dose,and/or the post-exposure dose is about 230 to about 399 mg and isadministered about once every four days. In further embodiments, theinitial dose, the primary dose, and/or the post-exposure dose is about230, about 235, about 240, about 245, about 250, about 255, about 260,about 265, about 270, about 275, about 280, about 285, about 290, about295, about 300, about 305, about 310, about 315, about 320, about 325,about 330, about 335, about 340, about 345, about 350, about 355, about360, about 365, about 370, about 375, about 380, about 385, about 390,or about 395 mg and is administered once every four days. In otherembodiments, the initial dose, the exposure dose, the primary dose,and/or the post-exposure dose is about 53 to about 285 mg and isadministered about once every five days. In some embodiments, theinitial dose, the exposure dose, the primary dose, and/or thepost-exposure dose is about 55, about 60, about 65, about 70, about 75,about 80, about 85, about 90, about 95, about 100, about 105, about 110,about 115, about 120, about 125, about 130, about 135, about 140, about145, about 150, about 155, about 160, about 165, about 170, about 175,about 180, about 185, about 190, about 200, about 205, about 210, about215, about 220, about 225, about 230, about 235, about 240, about 245,about 250, about 255, about 260, about 265, about 270, about 275, orabout 280 mg and is administered about once every five days. In stillother embodiments the initial dose, the primary dose, and/or thepost-exposure dose is about 285 to about 399 mg and is administered onceevery five days. In other embodiments, the initial dose, the primarydose, and/or the post-exposure dose is about 285, about 290, about 295,about 300, about 305, about 310, about 315, about 320, about 325, about330, about 335, about 340, about 345, about 350, about 355, about 360,about 365, about 370, about 375, about 380, about 385, about 390, orabout 395 mg and is administered once every five days. In furtherembodiments, the initial dose, the exposure dose, the primary dose,and/or the post-exposure dose is about 64 to about 342 mg and isadministered about once every six days. In some embodiments, the initialdose, the exposure dose, the primary dose, and/or the post-exposure doseis about 70, about 75, about 80, about 85, about 90, about 95, about100, about 105, about 110, about 115, about 120, about 125, about 130,about 135, about 140, about 145, about 150, about 155, about 160, about165, about 170, about 175, about 180, about 185, about 190, about 200,about 205, about 210, about 215, about 220, about 225, about 230, about235, about 240, about 245, about 250, about 255, about 260, about 265,about 270, about 275, about 280, about 285, about 290, about 295, about300, about 305, about 310, about 315, about 320, about 325, about 330,about 335, or about 340 mg and is administered about once every sixdays. In still other embodiments, the initial doses, the primary dose,and/or the post-exposure dose is about 342 to about 399 mg and isadministered about once every six days. In other embodiments, theinitial dose, the primary dose, and/or the post-exposure dose is about345, about 350, about 355, about 360, about 365, about 370, about 375,about 380, about 385, about 390, or about 395 mg and is administeredonce every six days. In yet other embodiments, the initial dose, theexposure dose, the primary dose, and/or the post-exposure dose is about75 to about 399 mg and is administered about once every week. In someembodiments, the initial dose, the exposure dose, the primary dose,and/or the post-exposure dose is about 80, about 85, about 90, about 95,about 100, about 105, about 110, about 115, about 120, about 125, about130, about 135, about 140, about 145, about 150, about 155, about 160,about 165, about 170, about 175, about 180, about 185, about 190, about200, about 205, about 210, about 215, about 220, about 225, about 230,about 235, about 240, about 245, about 250, about 255, about 260, about265, about 270, about 275, about 280, about 285, about 290, about 295,about 300, about 305, about 310, about 315, about 320, about 325, about330, about 335, about 340, about 345, about 350, about 355, about 360,about 365, about 370, about 375, about 380, about 385, about 390, orabout 395 mg and is administered about once every week.

In one embodiment, the post-exposure doses are administered at intervalsof about once per day for one to three days. In other embodiments, thepost-exposure doses are administered at intervals of about once per dayfor one to three weeks. In further embodiments, the post-exposure dosesare administered at intervals of about once every two to six days. Inother embodiments, the post-exposure doses are administered at intervalsof about every two days. In another embodiment, the post-exposure dosesare administered at intervals of about every three days. In yet otherembodiments, the post-exposure doses are administered at intervals ofabout every four days. In further embodiments, the post-exposure dosesare administered at intervals of about every five days. In still otherembodiments, the post-exposure doses are administered at intervals ofabout every six days. In other embodiments, the post-exposure doses areadministered at intervals of about once a week. In further embodimentsof the invention, the post-exposure doses are administered one, two, orthree times. In other embodiments, the post-exposure doses areadministered for about one week, about two weeks, or about three weeks.In another embodiment, the post-exposure doses are administered forabout one to three weeks. In yet other embodiments, the post-exposuredoses are administered for at least three weeks after exposure to atleast one species of Plasmodium. In further embodiments, thepost-exposure doses are divided doses that are administered about two toabout four times per day. In yet other embodiments, the post-exposuredoses are divided doses that are administered about 2, 3, or 4 times perday.

In certain embodiments, the post-exposure doses are administered forabout 1-21 days. In other embodiments, the post-exposure doses areadministered for about 1-14 days, 1-10 days, 1-7 days, 1-5 days, or 1-3days. In yet other embodiments, the post-exposure doses are administeredfor about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 days.

In one embodiment, the primary doses are administered at intervals ofabout once per day. In further embodiments, the primary doses areadministered at intervals of about once every two to six days. In otherembodiments, the primary doses are administered at intervals of aboutevery two days. In some embodiments, the primary doses are administeredat intervals of about every three days. In yet other embodiments, theprimary doses are administered at intervals of about every four days. Inanother embodiment, the primary doses are administered at intervals ofabout every five days. In still another embodiment, the primary dosesare administered at intervals of about every six days. In otherembodiments, the primary doses are administered at intervals of aboutonce a week. In other embodiments, the primary doses are administeredfor about one week, about two weeks, or about three weeks. In anotherembodiment, the primary doses are administered for about one to threeweeks. In yet other embodiments, the primary doses are administered forat least three weeks. In further embodiments, the primary doses areadministered at least three times. In yet other embodiments, the primarydoses are divided doses that are administered about two to about fourtimes per day. In yet other embodiments, the primary doses are divideddoses that are administered about 2, 3, or 4 times per day.

In certain embodiments, the primary doses are administered for about1-21 days. In other embodiments, the primary doses are administered forabout 1-14 days, 1-10 days, 1-7 days, 1-5 days, or 1-3 days. In yetother embodiments, the primary doses are administered for about 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21days.

In certain embodiments, the total amount of the initial doseadministered does not exceed about 900, 600, 500, or 400 mg prior topotential exposure of at least one species of Plasmodium. In otherembodiments, the total average weekly exposure dose does not exceedabout 200 mg. In further embodiments, the total average weekly exposuredose does not exceed 299 mg.

In certain embodiments, the initial dose is about 40-100 mg administeredonce per day for six days, followed by the exposure dose of about 12 mg,about 15 mg, about 20 mg, about 25 mg, about 30 mg, or about 35 mg,about 40 mg, or about 42 mg administered once per day during potentialexposure to at least one species of Plasmodium. In other embodiments,the initial dose is between about 34 and 85 mg administered once per dayfor seven days, followed by the exposure dose of about 12 mg, about 15mg, about 20 mg, about 25 mg, about 30 mg, about 35 mg, about 40 mg, orabout 42 mg administered once per day during potential exposure to atleast one species of Plasmodium. In other embodiments, the initial doseis between about 48 and 120 mg administered once per day for five days,followed by the exposure dose of about 12 mg, about 15 mg, about 20 mg,about 25 mg, about 30 mg, about 35 mg, about 40 mg, or about 42 mgadministered once per day during potential exposure to at least onespecies of Plasmodium. In other embodiments, the initial dose is betweenabout 60 and 150 mg administered once per day for four days, followed bythe exposure dose of about 12 mg, about 15 mg, about 20 mg, about 25 mg,about 30 mg, about 35 mg, about 40 mg, or about 42 mg administered onceper day during potential exposure to at least one species of Plasmodium.In other embodiments, the initial dose is between about 80 and 200 mgadministered once per day for three days, followed by the exposure doseof about 12 mg, about 15 mg, about 20 mg, about 25 mg, about 30 mg,about 35 mg, about 40 mg, or about 42 mg administered once per dayduring potential exposure to at least one species of Plasmodium. Inother embodiments, the initial dose is between about 30-35 mgadministered once per day for seven days, followed by the exposure doseof about 30-35 mg administered once per day during potential exposure toat least one species of Plasmodium.

In other embodiments, the initial dose of about 100 mg is administeredonce per day for six days, followed by the exposure dose of about 100 mgadministered once every four days during potential exposure to at leastone species of Plasmodium.

In various embodiments, the post-exposure dose is administered. Infurther embodiments, the post-exposure dose is administered one or moretimes, e.g., one, two, or at least three times. In further embodiments,the total weekly amount of administered exposure dose is between about75 and about 175 mg and the post-exposure dose is administered. In yetother embodiments, the total weekly amount of administered exposure doseis between about 175 mg and 195 mg and the post-exposure dose is notadministered.

In the various embodiments, the human subject can be a malaria-naïve andG6PD-normal adult or a child.

In certain embodiments, the administration of the initial dose, exposuredose, post-exposure dose, and/or primary dose is in a suitableformulation based upon the human subject's body weight and/or age. Infurther embodiments, the human subject has a low body weight. In stillother embodiments, the initial dose, the exposure dose, thepost-exposure dose, and/or the primary dose are administered inconcentration amounts of mg/kg based upon the individual subject'sweight, for example about 1-5 mg/kg.

The compound of Formula (I) is represented by the following structure:

or a pharmaceutically acceptable salt thereof.

In preferred embodiments, the compound of Formula (I) is Tafenoquine(TQ), a pharmaceutically acceptable salt of Tafenoquine, or isrepresented by the following structure:

In certain embodiments, the initial doses are the same as either theexposure doses or the post-exposure doses, while in other embodimentsthe initial doses differ from either the exposure doses or thepost-exposure doses. In further embodiments, the exposure doses are thesame as the post-exposure doses, while in other embodiments the exposuredoses differ from the post-exposure doses. In yet other embodiments, theprimary doses are the same as the post-exposure doses, while in otherembodiment the primary doses differ from the post-exposure doses.

In certain embodiments, for a malaria-naïve and G6PD-normal humansubject, the initial doses of a compound of Formula (I), apharmaceutically acceptable salt of Formula (I), or a pharmaceuticalcomposition comprising a compound of Formula (I) can be between about 75to about 399 mg. In other embodiments, the initial doses can be about100-399 mg, about 150-399 mg, about 200-399 mg, or about 250-399 mg. Infurther embodiments, the initial doses can be about 75 mg, about 100 mg,about 125 mg, about 150 mg, about 175 mg, about 190 mg, about 200 mg,about 210, about 225 mg, about 250 mg, about 275 mg, about 300 mg, about325 mg, about 350 mg, about 375 mg, or about 399 mg. In a furtherembodiment, the initial doses in a human subject are between about 350and about 399 mg. In another embodiment, the initial doses in a humansubject are between about 300 and about 350 mg. In yet anotherembodiment, the initial doses in a human subject are between about 250and about 300 mg. In further embodiment, the initial doses in a humansubject are between about 200 and about 250 mg. In yet anotherembodiment, the initial doses in a human subject are between about 210and about 250 mg. In another embodiment, the initial doses of a compoundof Formula (I) in a human subject are between about 150 and about 200mg. In yet other embodiments, the initial doses of a compound of Formula(I) in a human subject are between about 175 and about 195. In furtherembodiments of the invention, the initial doses in a human subject arebetween about 190 and about 150 mg. In further embodiment, the initialdoses in a human subject are between about 100 and about 150 mg. Inanother embodiment, the initial doses in a human subject are betweenabout 75 and about 125 mg.

The exposure doses of a compound of Formula (I), a pharmaceuticallyacceptable salt of Formula (I), or a pharmaceutical compositioncomprising a compound of Formula (I) is administered to a malaria-naïveand G6PD-normal human subject can total between about 75 and about 399mg in a week. In further embodiments, a total of about 75 mg, about 100mg, about 125 mg, about 150 mg, about 175 mg, about 190 mg, about 200mg, about 210 mg, about 225 mg, about 250 mg, about 275 mg, about 300mg, about 325 mg, about 350 mg, about 375 mg, or about 399 mg of theexposure dose is administered to the human subject in a week. In oneembodiment, a total of about 350 to about 399 mg of the exposure dose isadministered to a human subject in a week. In another embodiment, atotal of about 300 to about 350 mg of the exposure dose is administeredto a human subject in a week. In further embodiment, a total of about250 to about 300 mg of the exposure dose is administered to a humansubject in a week. In another embodiment, a total of about 200 to about250 mg of the exposure dose is administered to a human subject in aweek. In further embodiment, a total of about 210 to about 250 mg of theexposure dose is administered to a human subject in a week. In yetanother embodiment, a total of about 150 to about 200 mg of the exposuredose is administered to a human subject in a week. In anotherembodiment, a total of about 150 to about 190 mg of the exposure dose isadministered to a human subject in a week. In further embodiment, atotal of about 100 to about 150 mg of the exposure dose of a compound isadministered to a human subject in a week. In an additional embodiment,a total of about 125 to about 175 mg of the exposure dose isadministered to a human subject in a week. In another embodiment, atotal of about 175 to about 195 mg of the exposure dose is administeredto a human subject in a week. In other embodiments, a total of about 75to about 125 mg of the exposure dose is administered to a human subjectin a week. In yet another embodiment, a total of about 150 mg of theexposure dose is administered to a human subject in a week.

The post-exposure doses of a compound of Formula (I), a pharmaceuticallyacceptable salt of Formula (I), or a pharmaceutical compositioncomprising a compound of Formula (I) in a malaria-naïve and G6PD-normalhuman subject can be between about 75 and about 399 mg. In otherembodiments, the post-exposure doses can be about 75-299 mg, about100-299 mg, about 150-299 mg, about 200-299 mg, about 100-399 mg, about150-399 mg, about 200-399 mg, or about 250-399 mg. In furtherembodiments, the post-exposure doses can be about 75 mg, about 100 mg,about 125 mg, about 150 mg, about 175 mg, about 190 mg, about 200 mg,about 210 mg, about 225 mg, about 250 mg, about 275 mg, about 300 mg,about 325 mg, about 350 mg, about 375 mg, or about 399 mg. In a furtherembodiment, the post-exposure doses in a human subject are between about350 to about 399 mg. In another embodiment, the post-exposure doses in ahuman subject are between about 300 and about 350 mg. In yet anotherembodiment, the post-exposure doses in a human subject are between about250 and about 300 mg. In further embodiment, the post-exposure doses ina human subject are between about 200 and about 250 mg. In yet anotherembodiment, the post-exposure doses in a human subject are between about210 and about 250 mg. In another embodiment, the post-exposure doses ina human subject are between about 150 and about 200 mg. In furtherembodiments of the invention, the post-exposure doses in a human subjectare between about 150 and about 190 mg. In yet other embodiments, thepost-exposure doses in a human subject are between about 175 and about195 mg. In another embodiment, the post-exposure doses in a humansubject are between about 75 and about 125. In further embodiment, thepost-exposure doses in a human subject are between about 100 and about150 mg.

In certain embodiments, for a malaria-naïve and G6PD-normal humansubject, the primary doses of a compound of Formula (I), apharmaceutically acceptable salt of Formula (I), or a pharmaceuticalcomposition comprising a compound of Formula (I) can be between about 75to about 399 mg. In other embodiments, the primary doses can be about75-299 mg, about 100-299 mg, about 150-299 mg, about 200-299 mg, about100-399 mg, about 150-399 mg, about 200-399 mg, or about 250-399 mg. Infurther embodiments, the primary doses can be about 75 mg, about 100 mg,about 125 mg, about 150 mg, about 175 mg, about 190 mg, about 200 mg,about 210 mg, about 225 mg, about 250 mg, about 275 mg, about 300 mg,about 325 mg, about 350 mg, about 375 mg, or about 399 mg. In a furtherembodiment, the primary doses in a human subject are between about 350and about 399 mg. In another embodiment, the primary doses in a humansubject are between about 300 and about 350 mg. In yet anotherembodiment, the primary doses in a human subject are between about 250and about 300 mg. In further embodiment, the primary doses in a humansubject are between about 200 and about 250 mg. In yet anotherembodiment, the primary doses in a human subject are between about 210and about 250 mg. In other embodiments, the primary doses in a humansubject are between about 175 and about 195 mg. In another embodiment,the primary doses in a human subject are between about 150 and about 200mg. In further embodiments of the invention, the primary doses in ahuman subject are between about 150 and about 190 mg. In furtherembodiment, the primary doses in a human subject are between about 100and about 150 mg. In still another embodiment, the primary doses in ahuman subject are between about 75 and about 125 mg.

In one embodiment, the initial doses are administered one to three weeksprior to potential exposure to at least one species of Plasmodium. Inanother embodiment, the initial doses are administered at least threedays prior to potential exposure to at least one species of Plasmodium.In yet other embodiments, the initial doses are administered one, two,three, or at least three times prior to potential exposure to at leastone species of Plasmodium.

In one embodiment, the post-exposure doses are administered one to threeweeks after potential exposure to at least one species of Plasmodium. Inanother embodiment, the post-exposure doses are administered at leastthe three days after potential exposure to at least one species ofPlasmodium. In yet other embodiments, the post-exposure doses areadministered at least three times after potential exposure to at leastone species of Plasmodium.

The compounds or pharmaceutical compositions of the present inventioncan be administered orally or sublingually. In one embodiment, the routeof administration is oral. In yet another embodiment, the route ofadministration is sublingual.

The compounds or pharmaceutical compositions of the present inventioncan be administered as a single or as a divided dose. In someembodiments, the doses can be single, divided, or a combination thereof.For the initial doses, the exposure doses, the primary dose, and/or thepost-exposure doses in one embodiment, the human subject is administereda divided dose of from about 12 to about 399 mg of a compound of Formula(I), or a pharmaceutical composition. In some embodiments of theinvention, the human subject is administered a divided dose of theinitial dose, the exposure dose, the primary dose, and/or thepost-exposure dose about two to about four times a day.

The invention also relates to methods of preventing malaria by achievingand maintaining a steady state Cmin serum or plasma concentration ofbetween about 50 ng/mL and about 800 ng/mL of Formula (I) or tafenoquinein approximately 90% of malaria-naïve, G6PD-normal adult or childsubjects. In another aspect, methods of preventing malaria compriseachieving a steady state Cmin serum or plasma concentration of at leastabout 50 ng/mL to about 400 ng/mL prior to potential exposure of atleast one species of Plasmodium. In certain embodiments, the steadystate Cmin serum or plasma concentration is at least about 80 ng/mL toabout 200 ng/mL prior to potential exposure of at least one species ofPlasmodium. In other embodiments, the steady state Cmin serum or plasmaconcentration is at least about 100 ng/mL to about 175 ng/mL prior topotential exposure of at least one species of Plasmodium. In furtherembodiments, the steady state Cmin serum or plasma concentration of atleast about 50 ng/mL to about 400 ng/mL is maintained throughout theperiod of potential exposure of at least one species of Plasmodium. Inother embodiments, the steady state Cmin serum or plasma concentrationof at least about 80 ng/mL to about 200 ng/mL is maintained throughoutthe period of potential exposure of at least one species of Plasmodium.In additional embodiments, the steady state Cmin serum or plasmaconcentration of at least about 100 ng/mL to about 175 ng/mL ismaintained throughout the period of potential exposure of at least onespecies of Plasmodium. In yet another embodiment, the steady state Cminserum or plasma concentration of at least about 50 ng/mL to about 400ng/mL is maintained for at least three weeks after potential exposure ofat least one species of Plasmodium. In other embodiments, the steadystate Cmin serum or plasma concentration of at least about 80 ng/mL toabout 200 ng/mL is maintained for at least three weeks after potentialexposure of at least one species of Plasmodium. In further embodiments,the steady state Cmin serum or plasma concentration of at least about100 ng/mL to about 175 ng/mL is maintained for at least three weeksafter potential exposure of at least one species of Plasmodium. Infurther embodiment, prior to potential exposure, throughout the periodof potential exposure, and/or for at least three weeks after potentialexposure, the steady state Cmin serum or plasma concentration achievedand maintained in a malaria-naïve, G6PD-normal adult or child subject isbetween about 80 ng/mL to about 600 ng/mL of a compound of Formula (I)or tafenoquine. In another embodiment, a steady state Cmin serum orplasma concentration achieved and maintained for at least three weeksafter potential exposure in a malaria-naïve, G6PD-normal adult or childsubject is between about 80 ng/mL to about 400 ng/mL of a compound ofFormula (I) or tafenoquine. In yet another embodiment, a steady stateCmin serum or plasma concentration achieved and maintained for at leastthree weeks after potential exposure in a malaria-naïve, G6PD-normaladult or child subject is between about 80 ng/mL to about 200 ng/mL of acompound of Formula (I) or tafenoquine. In another embodiment, a steadystate Cmin serum or plasma concentration achieved and maintained for atleast three weeks after potential exposure in a malaria-naïve,G6PD-normal adult or child subject is at least about 80 ng/mL of acompound of Formula (I) or tafenoquine. In other embodiments, a steadystate Cmin serum or plasma concentration achieved and maintained for atleast three weeks after potential exposure in a malaria-naïve,G6PD-normal adult or child subject is at least about 50 ng/mL, 80 ng/mL,100 ng/mL, 125 ng/mL, 150 ng/mL, or 175 ng/mL of a compound of Formula(I) or tafenoquine. In certain embodiments, prior to exposure,throughout the period of exposure, and/or for at least three weeks afterexposure, a steady state Cmin serum or plasma concentration achieved ina subject is at least about 50 ng/mL, 80 ng/mL, 100 ng/mL, 125 ng/mL,150 ng/mL, or 175 ng/mL of a compound of Formula (I) or tafenoquine. Incertain aspects, the Cmin is measured as the median Cmin of a populationof subjects. In other aspects, the Cmin is measured as the 5^(th)percentile Cmin of a population of subjects. In still other aspects, theserum or plasma concentration of a compound of Formula (I) ortafenoquine is measured in the individual subject.

The invention is also directed to methods of preventing malariacomprising administering a pharmaceutical composition comprising acompound of Formula (I) or tafenoquine according to any one of thedosing regimens described herein. The disclosed compounds of Formula (I)or tafenoquine can be administered to the subject in conjunction with anacceptable pharmaceutical carrier or diluent as part of a pharmaceuticalcomposition for prevention of malaria. The invention is further directedtoward kits for administering the disclosed dosing regimens or forcarrying the disclosed methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings.

FIG. 1 Goodness-of-fit plots of plasma tafenoquine concentrations forthe final pharmacokinetic model. The solid line represents the line ofidentity.

FIG. 2 Visual predictive check of model-predicted vs. observed plasmaconcentrations of tafenoquine.

FIG. 3 Plasma concentration-time profile for tafenoquine following theReference Regimen. The Reference Regimen consists of initial doses of200 mg once daily for three days prior to exposure, followed by exposuredoses of 200 mg once per week during exposure, and post-exposure dosesof 200 mg once per week for three weeks post-exposure. The hashedhorizontal line represents the 80 ng/mL concentration threshold. Theleft hashed vertical line represent when deployment and exposure dosesbegin. The period of time prior to the left hashed vertical lineindicates the time during which initial doses are given. The righthashed vertical line represents when deployment ends and post-exposuredosing beings. Each peak represents the maximum concentration followingadministration of each new dose. FIG. 3 depicts the predicted 95^(th)percentile, median, and 5^(th) percentile plasma tafenoquineconcentrations for a hypothetical oral intake of tafenoquine forapproximately six months of potential exposure to at least one speciesof Plasmodium, in which the regimen included an initial dose (200 mgonce per day for three days), weekly exposure doses (200 mg), followedby three once weekly post-exposure doses (200 mg). This regimenmaintains the 5th percentile tafenoquine concentrations at or above 80ng/ml until approximately 3.5-4.5 weeks post-exposure. 80 ng/ml,depicted as a dotted horizontal line, is the threshold required forprotection against development of symptomatic malaria in malaria-naïve,G6PD-normal individuals. Therefore, this dose is protective becausemedian drug levels are higher than the 80 ng/ml threshold throughoutdeployment. The use of three once weekly post-exposure prophylaxis dosesof 200 mg following potential exposure to at least one species ofPlasmodium maintains drugs levels above 80 ng/ml at the 5^(th)percentile for several weeks post-deployment to prevent symptomaticmalaria arising from a late deployment exposure to a species ofPlasmodium.

FIG. 4 Tafenoquine plasma concentration-time profiles (median) for theReference Regimen at different body weights. The Reference Regimenconsists of initial doses of 200 mg once daily for three days prior toexposure, followed by exposure doses of 200 mg once per week duringexposure, and post-exposure doses 200 mg once per week for three weekspost-exposure. The hashed horizontal line represents the 80 ng/mLconcentration threshold. The left hashed vertical line represents whendeployment and exposure doses begin. The period of time prior to theleft hashed vertical line indicates the time during which initial dosesare given. The right hashed vertical line represents when deploymentends and post-exposure dosing beings. Each peak represents the maximumconcentration following administration of each new dose. This shows thatthe reference regimen is protective at different body weights becausethe median concentrations are always higher than the protectivethreshold concentrations.

FIG. 5 Tafenoquine plasma concentration-time profiles (median) for theReference Regimen in fed and fasted individuals. The Reference Regimenconsists of initial doses of 200 mg once daily for three days prior toexposure, followed by exposure doses of 200 mg once per week duringexposure, and post-exposure doses 200 mg once per week for three weekspost-exposure. The hashed horizontal line represents the 80 ng/mLconcentration threshold. The left hashed vertical line represents whendeployment and exposure doses begin. The period of time prior to theleft hashed vertical line indicates the time during which initial dosesare given. The right hashed vertical line represents when deploymentends and post-exposure dosing beings. Each peak represents the maximumconcentration following administration of each new dose. This shows thatthe Reference Regimen is effective either in the fed or the fastedstate, because median drug concentrations are higher the 80 ng/mlprotective threshold.

FIG. 6 Tafenoquine plasma concentration-time profiles (median) of theReference Regimen in individuals of different ages. The ReferenceRegimen consists of initial doses of 200 mg once daily for three daysprior to exposure, followed by exposure doses of 200 mg once per weekduring exposure, and post-exposure doses 200 mg once per week for threeweeks post-exposure. The hashed horizontal line represents the 80 ng/mLconcentration threshold. The left hashed vertical line represent whendeployment and exposure doses begin. The period of time prior to theleft hashed vertical line indicates the time during which initial dosesare given. The right hashed vertical line represents when deploymentends and post-exposure dosing beings. Each peak represents the maximumconcentration following administration of each new dose. This shows thatthe Reference Regimen is effective across different age ranges becausethe median concentrations are always higher the 80 ng/ml protectivethreshold during deployment.

FIG. 7 Tafenoquine plasma concentration-time profiles (mean) followingdifferent regimens. Regimen 1 consists of 200 mg administered onceweekly without an initial dose and Regimen 2 consists of 100 mgadministered once weekly without an initial dose. Regimen 3 consists ofan initial dose of 200 mg once daily for three days followed by a weeklydose of 200 mg for approximately five and a half months followed bythree once-daily post-exposure doses. Regimen 4 consists of an initialdose administered once daily for three days followed by one weekly doseof 400 mg followed by a monthly exposure dose of 400 mg. Regimen 4 issimilar to the dosing in the Walsh et. al. Thai marine study and wasused for comparison purposes. Regimen 5 consists of a weekly dose of 400mg following an initial dose of 400 mg once daily for three days.Regimen 6 consists of 150 mg administered once weekly without an initialdose and Regimen 7 consists of 50 mg administered once weekly without aninitial dose. The hashed horizontal line represents the 80 ng/mLconcentration threshold. The left hashed vertical line represents whendeployment and exposure doses begin. The period of time prior to theleft hashed vertical line indicates the time during which initial dosesare given. The right hashed vertical line represents when deploymentends and post-exposure dosing beings. Each peak represents the maximumconcentration following administration of each new dose.

Based on these profiles drawn in FIG. 7 and described on the prior page,the following conclusions can be drawn:

(i) Modification of the invention depicted in FIG. 3, by removing theinitial dose (Regimen 1) maintains median minimum concentrations abovethe threshold provided that dosing is initiated at least three weeksprior to exposure. Modifying the Reference Regimen to allowadministration of three doses of 200 mg not more than one week apartprior to potential exposure (rather than simply once per day) to atleast one species of Plasmodium, will be better tolerated and reduce therisk of hemolytic anemia in G6PD, since the threshold dose consideredsafe in G6PD-deficient individuals is 300 mg. This general observation,that removing the initial dose maintains protection at the desired levelis also true of other regimens, that are not 200 mg (see below),provided that dosing is initiated at an appropriate time prior totravel, deployment, or potential exposure to at least one species ofPlasmodium.

(ii) Modification of the invention depicted in FIG. 3, by lowering theexposure dose to 100 or 150 mg (Regimens 2 or 6), does maintain medianconcentrations above the threshold for protection after two or threeweekly doses. Simulation of the prophylactic monthly regimen of 400 mg(Regimen 4) predicted that median steady-state trough plasma tafenoquineconcentrations above the threshold for protection did not persist forthe entire simulated deployment and were lower than those of thereference regimen (FIG. 3). In the simulation in which 50 mg was givenweekly with no initial dose (Regimen 7), median steady state troughconcentrations never exceeded the intended threshold. Therefore therange of possible marketed doses is between 75-399 mg over the timeperiod of a week (since Regimen 5, 400 mg, is poorly tolerated).

FIG. 8 Tafenoquine plasma concentration-time profiles (95^(th), median,and 5^(th) percentiles) for additional time points. The extendedReference Regimen is the Reference Regimen viewed for an additionalthree weeks. The Reference Regimen consists of initial doses of 200 mgonce daily for three days prior to exposure, followed by exposure dosesof 200 mg once per week during exposure, and post-exposure doses 200 mgonce per week for three weeks post-exposure (FIG. 3). Regimen 3, alsoreferred to as reverse load, consists of 200 mg once-weekly dosesfollowed by three once-daily doses. The hashed horizontal linerepresents the 80 ng/mL concentration threshold. The hashed verticalline represents when deployment ends. The area to the left of the hashedvertical line represents deployment and exposure doses. The area to theright of the hashed vertical line represents post-exposure dosing. Eachpeak represents the maximum concentration following administration ofeach new dose. This figure depicts the predicted 95^(th), median, and5^(th) percentile tafenoquine plasma concentrations at the dose leveldepicted in FIG. 3 (solid lines) or a modified regimen (the ‘reverseload’ where the post-exposure dosing regimen is 200 mg once per day forthree days, also Regimen 3 in FIG. 7). These regimens maintain plasmaconcentrations above the desired threshold for 2.5-3.5 weeks. Thereverse load (Regimen 3) may be more convenient than post-exposuredosing once per week for three weeks. Since the peak observed after thereverse load is lower than that observed after dosing at 400 mg once perday for three days (see Regimen 5 in FIG. 7), it is expected to bebetter tolerated than the 400 mg regimen.

FIG. 9 Tafenoquine plasma concentration-time profiles. Profiles aredepicted for a Daily Regimen (100 mg once per day for six days followedby 25 mg once per day for an approximately three month period during theperiod of exposure). For the purposes of comparison, profiles aredepicted for the Reference Regimen (initial pre-exposure doses of 200 mgonce per day for three days, followed by exposure doses of 200 mg perweek during the period of exposure, and no post-exposure dose). Thehashed horizontal line represents the 80 ng/mL concentration threshold.The hashed left vertical line represents when exposure dosing beings.The period of time prior to the left hashed vertical line indicates theinitial doses. The right hashed vertical line represents when deploymentends for the Reference Regimen and the dotted vertical line representswhen deployment ends for the Daily Regimen. Each peak indicates that adose has been administered. The figure depicts an alternate way, viadaily administration, of achieving steady state in a manner that islikely to improve gastrointestinal tolerability due to a reduction inthe bolus dose of tafenoquine given at each dosing event (e.g., from 200mg to 100 mg and 25 mg). Also it shows that with the Reference Regimen,and with this particular Daily Regimen, that post-exposure dosing is notrequired to maintain a median plasma concentration of at least 80 ng/mLfor at least 3 weeks post-exposure.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

Definitions

All definitions of substituents set forth below are further applicableto the use of the term in conjunction with another substituent. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which this invention belongs.

As used herein, the singular forms “a,” “and,” and “the” include pluralreference unless the context clearly dictates otherwise. Additionally,the term “comprises” is intended to include embodiments where themethod, apparatus, composition, etc., consists essentially of and/orconsists of the listed steps, components, etc. Similarly, the term“consists essentially of” is intended to include embodiments where themethod, apparatus, composition, etc., consists of the listed steps,components, etc.

As used herein, the term “about” refers to a number that differs fromthe given number by less than 10%. In other embodiments, the term“about” indicates that the number differs from the given number by lessthan 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1%.

As used herein, “Cmin” refers to the minimum concentration that a drugachieves after the drug has been administered and prior to theadministration of a second or additional dose. Further, “Cmax,” as usedherein, refers to the maximum concentration.

As used herein, “exposure dose” refers to the dose(s) which isadministered during potential exposure to at least one species ofPlasmodium. Further, “maintenance dose” and “exposure dose” have thesame meaning and are used interchangeably herein.

As used herein, “G6PD-normal” refers to human subjects with normallevels of glucose-6-phosphate dehydrogenase. Normal levels of G6PD maybe determined by approved laboratory tests using validated methodologyknown to those skilled in the art.

As used herein, “initial dose” refers to the dose(s) which isadministered prior to potential exposure to at least one species ofPlasmodium. Further, “loading dose,” “initial dose,” and “pre-exposuredose” have the same meaning and are used interchangeably herein.

As used herein, a “malaria-naïve” subject is defined operationally asreferring to a human child or adult subject, for whom a physician,nurse, or other qualified medical or public health professional mayreasonably assume has not previously experienced an episode ofsymptomatic malaria based on a review of travel and/or medical history.

As used herein, “non-immune” refers to individuals who have hadinsufficient prior exposure to malaria to render them immune to thesigns and symptoms of malaria when malaria parasites are confirmed bymicroscopy to be present. A non-immune individual may also bemalaria-naïve if they have never been exposed to malaria before.

“Pharmaceutically acceptable carrier” means non-therapeutic componentsthat are of sufficient purity and quality for use in the formulation ofa composition of the invention that, when appropriately administered,typically do not produce an adverse reaction, and that are used as avehicle for a drug substance (e.g., a compound of Formula (I)).

As used herein, “post-exposure dose” refers to the dose(s) which isadministered after potential exposure to at least one species ofPlasmodium.

As used herein, “post-exposure malaria” refers to malaria which iscaused from the latent stages of at least one species of Plasmodiumand/or wherein the symptoms of malaria begin after potential exposure ortravel.

As used herein, “potential exposure,” “deployment,” and “travel” refersto the period of time between entry and exit of a human subjectinto/from a geographical area where they may be exposed to Anophelesmosquitoes harboring human malaria parasites.

As used herein, “primary dose” refers to the dose(s) which isadministered prior to the post-exposure dose and may be administeredprior to or during potential exposure to at least one species ofPlasmodium, or after potential exposure but prior to becomingsymptomatic.

As used herein, “semi-immune” refers to a resident of a malaria-endemiccountry who, due to many prior exposures to symptomatic malaria, hasdeveloped a partial immunity that usually results in a lack of signs andsymptoms of clinical malaria when the presence of malaria parasites inthe blood is confirmed by microscopy.

As used herein, Formula (I) is “tafenoquine” and also includes thefollowing references to tafenoquine: Tafenoquine, Tafenoquine [INN:BAN],Etaquine, UNII-262P8GS9L9, C24H28F3N3O3, CHEBI:172505, AIDS006901,106635-81-8 (maleate), AIDS-006901, CID115358, SB-252263, WR 238605,WR-238605, WR238605, LS-172012, 1,4-Pentanediamine,N4-(2,6-dimethoxy-4-methyl-5-(3-(trifuluromethyl)phenoxy)-8-quinolinyl-,106635-80-7,N(4)-(2,6-Dimethoxy-4-methyl-5-((3-trifluromethyl)phenoxy)-8-quinolinyl)-1,4-pentanediamine,N-[2,6-dimethoxy-4-methyl-5-[3-(trifluoromethyl)phenoxy]quinolin-8-yl]diamine,(4-Amino-1-methylbutyl){2,6-dimethoxy-4-methyl-5-[3-(trifluoromethyl)phenoxy](8-quinoly)}amine,(R)—N3-(2,6-Dimethoxy-4-methyl-5-(3-trifluoromethyl)phenoxy)quinolin-8-yl)pentane-1,4-diamine,(RS)—N(sup3)-(2,6-Dimethoxy-4-methyl-5-(3-trifluoro-methylphenoxy)quinolin-8-yl)pentane-1,4-diamine.

Dosing Regimen

In certain embodiments, dosing is selected to provide a serum or plasmatafenoquine concentration of at least about 80 ng/mL. Doses above 400 mgare often not well tolerated (e.g., the dose may cause gastrointestinalissues or toxicity) by adult subjects regardless of the subjects' G6PDstatus. In G6PD normal adult subjects, doses of up to 400 mg may be welltolerated, while in G6PD deficient subjects, doses of 300 mg or more maynot be well tolerated.

In one aspect, the method comprises administering to the human subjectone or more initial dose(s) of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), for example, at leastonce per day for three days, once per week for one to three weeks, or atleast three times, prior to potential exposure of at least one speciesof Plasmodium, wherein each said initial dose is about 75 to about 299mg, followed by administering to the human subject an exposure dose of acompound of Formula (I), a pharmaceutically acceptable salt thereof, ora pharmaceutical composition comprising a compound of Formula (I), oneor more times per week, for example once per day, once every two to sixdays, or once per week during potential exposure of at least one speciesof Plasmodium, wherein the total administered amount of the exposuredose is about 75 to about 299 mg per week, followed by administering tothe human subject a post-exposure dose of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), for example, at leastonce per day for three days, once per week for three weeks, or at leastthree times, after potential exposure of at least one species ofPlasmodium; wherein each said post-exposure dose is about 75 to about299 mg, wherein the human subject is malaria-naïve andGlucose-6-phosphate dehydrogenase (G6PD) normal, and wherein Formula (I)has the following structure,

Alternativename:-[2,6-Dimethoxy-4-methyl-5-[3-(trifluoromethyl)phenoxy]quinolin-8-yl]pentane-1,4-diamine.

A pharmaceutically acceptable salt thereof, including,

CAS number for above identified structure of succinate salt 106635-81-8.

The compounds of the invention useful for practicing the methodsdescribed herein may possess one or more chiral centers and so exist ina number of stereoisomeric forms. All stereoisomers and mixtures thereofare included in the scope of the present invention. Racemic compoundsmay either be separated using preparative HPLC and a column with achiral stationary phase or resolved to yield individual enantiomersutilizing methods known to those skilled in the art. In addition, chiralintermediate compounds may be resolved and used to prepare chiralcompounds of the invention.

The compounds described herein may exist in one or more tautomericforms. All tautomers and mixtures thereof are included in the scope ofthe present invention.

The compounds of the present invention can be administered as the freebase or as a pharmaceutically acceptable salt. For example, an acid saltof a compound of the present invention containing an amine or otherbasic group can be obtained by reacting the compound with a suitableorganic or inorganic acid, resulting in pharmaceutically acceptableanionic salt forms. Examples of anionic salts include the acetate,benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, calciumedetate, camsylate, carbonate, chloride, citrate, dihydrochloride,edetate, edisylate, estotate, esylate, fumarate, glyceptate, gluconate,glutamate, glycollylarsanilate, hexylresorcinate, hydrobromide,hydrochloride, hydroxynaphthoate, iodide, isethionate, lactate,lactobionate, malate, maleate, mandelate, mesylate, methylsulfate,mucate, napsylate, nitrate, pamoate, pantothenate,phosphate/diphosphate, polygalacturonate, salicylate, stearate,subacetate, succinate, sulfate, tannate, tartrate, teoclate, tosylate,and triethiodide salts. In one embodiment, the compound of Formula (I)is a hydrochloride salt.

The invention is also directed to methods of the invention using apharmaceutical composition comprising a compound of Formula (I), or apharmaceutically acceptable salt thereof. The disclosed compounds ofFormula (I), or a pharmaceutically available salt thereof can beadministered to the subject in conjunction with an acceptablepharmaceutical carrier or diluent as part of a pharmaceuticalcomposition for prophylaxis of malaria, and according to any of thedosing regimens described herein. Formulation of the compound to beadministered will vary according to the route of administration selected(e.g., solution, emulsion, capsule). Suitable pharmaceutical carriersmay contain inert ingredients which do not interact with the compound.Standard pharmaceutical formulation techniques can be employed, such asthose described in Remington's Pharmaceutical Sciences, Mack PublishingCompany, Easton, Pa. Suitable pharmaceutical carriers for parenteraladministration include, for example, sterile water, physiologicalsaline, bacteriostatic saline (saline containing about 0.9% mg/ml benzylalcohol), phosphate-buffered saline, Hank's solution, Ringer's-lactateand the like. Methods for encapsulating compositions (such as in acoating of hard gelatin or cyclodextran) are known in the art (Baker, etal., “Controlled Release of Biological Active Agents”, John Wiley andSons, 1986).

In one embodiment, the pharmaceutical composition comprises apharmaceutically acceptable carrier or diluent and a compound of Formula(I), or a pharmaceutically acceptable salt thereof.

The methods of the invention prevent a human subject from havingmalaria. As used herein “preventing” or “prevention” refers to obtainingdesired pharmacological and/or physiological effects. The effect caninclude achieving, partially or substantially, one or more of thefollowing results: partially or totally avoiding the disease, disorder,or syndrome; or partially or totally avoiding clinical symptom orindicator associated with the disease, disorder, or syndrome.

The human subject may be an adult or a child. As used herein, a “child”refers to a human subject who is between the ages of 1 day to 17 years,364 days of age inclusive. The term “adult” refers to a human subjectwho is 18 years of age or older.

Example embodiments of initial doses, exposure doses, and post-exposuredoses in a human subject are shown in Table 1:

TABLE 1 Dosing Regimen for a Human Subject Initial dose Embodiment (mg)¹Exposure dose (mg)² Post-exposure dose (mg) ³ 1 40 75, 100, 125, 150,175, 190, 75, 100, 125, 150, 175, 190, 200, 210, 225, 250, 275, 200,210, 225, 250, 275, 300, 300, 325, 350, 375, or 399 325, 350, 375, or399 2 50 75, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175, 190, 200,210, 225, 250, 275, 200, 210, 225, 250, 275, 300, 300, 325, 350, 375, or399 325, 350, 375, or 399 3 75 75, 100, 125, 150, 175, 190, 75, 100,125, 150, 175, 190, 200, 210, 225, 250, 275, 200, 210, 225, 250, 275,300, 300, 325, 350, 375, or 399 325, 350, 375, or 399 4 100 75, 100,125, 150, 175, 190, 75, 100, 125, 150, 175, 190, 200, 210, 225, 250,275, 200, 210, 225, 250, 275, 300, 300, 325, 350, 375, or 399 325, 350,375, or 399 5 125 75, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175,190, 200, 210, 225, 250, 275, 200, 210, 225, 250, 275, 300, 300, 325,350, 375, or 399 325, 350, 375, or 399 6 150 75, 100, 125, 150, 175,190, 75, 100, 125, 150, 175, 190, 200, 210, 225, 250, 275, 200, 210,225, 250, 275, 300, 300, 325, 350, 375, or 399 325, 350, 375, or 399 7175 75, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175, 190, 200, 210,225, 250, 275, 200, 210, 225, 250, 275, 300, 300, 325, 350, 375, or 399325, 350, 375, or 399 8 190 75, 100, 125, 150, 175, 190, 75, 100, 125,150, 175, 190, 200, 210, 225, 250, 275, 200, 210, 225, 250, 275, 300,300, 325, 350, 375, or 399 325, 350, 375, or 399 9 200 75, 100, 125,150, 175, 190, 75, 100, 125, 150, 175, 190, 200, 210, 225, 250, 275,200, 210, 225, 250, 275, 300, 300, 325, 350, 375, or 399 325, 350, 375,or 399 10 210 75, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175, 190,200, 210, 225, 250, 275, 200, 210, 225, 250, 275, 300, 300, 325, 350,375, or 399 325, 350, 375, or 399 11 225 75, 100, 125, 150, 175, 190,75, 100, 125, 150, 175, 190, 200, 210, 225, 250, 275, 200, 210, 225,250, 275, 300, 300, 325, 350, 375, or 399 325, 350, 375, or 399 12 25075, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175, 190, 200, 210, 225,250, 275, 200, 210, 225, 250, 275, 300, 300, 325, 350, 375, or 399 325,350, 375, or 399 13 275 75, 100, 125, 150, 175, 190, 75, 100, 125, 150,175, 190, 200, 210, 225, 250, 275, 200, 210, 225, 250, 275, 300, 300,325, 350, 375, or 399 325, 350, 375, or 399 14 300 75, 100, 125, 150,175, 190, 75, 100, 125, 150, 175, 190, 200, 210, 225, 250, 275, 200,210, 225, 250, 275, 300, 300, 325, 350, 375, or 399 325, 350, 375, or399 15 325 75, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175, 190,200, 210, 225, 250, 275, 200, 210, 225, 250, 275, 300, 300, 325, 350,375, or 399 325, 350, 375, or 399 16 350 75, 100, 125, 150, 175, 190,75, 100, 125, 150, 175, 190, 200, 210, 225, 250, 275, 200, 210, 225,250, 275, 300, 300, 325, 350, 375, or 399 325, 350, 375, or 399 17 37575, 100, 125, 150, 175, 190, 75, 100, 125, 150, 175, 190, 200, 210, 225,250, 275, 200, 210, 225, 250, 275, 300, 300, 325, 350, 375, or 399 325,350, 375, or 399 18 399 75, 100, 125, 150, 175, 190, 75, 100, 125, 150,175, 190, 200, 210, 225, 250, 275, 200, 210, 225, 250, 275, 300, 300,325, 350, 375, or 399 325, 350, 375, or 399 19 75, 100, 75, 100, 125, or150 75, 100, 125, 150, 175, 190, 125, 150, 200, 210, 225, 250, 275, 300,175, 190, 325, 350, 375, or 399 200, 210, 225, 250, 275, 300, 325, 350,375, or 399 20 75, 100, 175, 190, 200, 210, 225, None 125, 150, 250,275, 300, 325, 350, 175, 190, 375, or 399 200, 210, 225, 250, 275, 300,325, 350, 375, or 399 ¹Initial dosing prior to potential exposure to atleast one species of Plasmodium for a) once per day for up to ten days,b) once per week for three weeks, c) once per week for one week, d) atleast three times, or e) divided doses thereof, including once everyfour days. ²Exposure dosing periodically during potential exposure to atleast one species of Plasmodium for a) once per week during period ofpotential exposure, b) once per day during period of potential exposure,wherein the total administered amount over a week is listed above, c)once every two to six days doses thereof, wherein the total administeredamount over a week is listed above, or d) divided doses thereof. ³Post-exposure dose administered after potential exposure to at least onespecies of Plasmodium for a) once per day for up to seven days,including once per day for three days b) once per week for three weeks,d) at least three times, or e) divided doses thereof, including onceevery four days.

In one embodiment of the invention, the compound of Formula (I) istafenoquine or a pharmaceutically acceptable salt thereof.

In certain embodiments of the invention, the malaria-naïve, G6PD-normalhuman subject is an adult or a child.

In yet another embodiment, a steady state Cmin serum or plasmaconcentration of between about 50 ng/mL to about 800 ng/mL oftafenoquine in a malaria naïve, G6PD-normal human subject is attained.In further embodiment, a steady state Cmin serum or plasma concentrationof between about 80 ng/mL to about 600 ng/mL of tafenoquine in a malarianaïve, G6PD-normal human subject is attained. In another embodiment, asteady state Cmin serum or plasma concentration of between about 80ng/mL to about 400 ng/mL of tafenoquine in a malaria naïve, G6PD-normalhuman subject is attained. In yet another embodiment, a steady stateCmin serum or plasma concentration of between about 80 ng/mL to about200 ng/mL of tafenoquine in a malaria naïve, G6PD-normal human subjectis attained. In another embodiment, a steady state Cmin serum or plasmaconcentration of about greater than or equal to 80 ng/mL of tafenoquinein a malaria naïve, G6PD-normal human subject is attained. In certainembodiments the 80 ng/mL Cmin concentration will be that of theindividual or of the median or 5^(th) percentile of a populationadministered the given dosing regimen.

In one embodiment of the invention, Plasmodium exposure comprises atleast one Plasmodium species selected from P. falciparum, P. vivax, P.ovale, P. malariae, and P. knowlesi.

In yet another embodiment, administering the compound, or thepharmaceutical composition, achieves a steady state Cmin serum or plasmaconcentration of at least about 80 ng/mL of a compound of Formula (I) ortafenoquine. In other embodiments, administering the compound, or thepharmaceutical composition, achieves a steady state Cmin serum or plasmaconcentration of at least about 80 ng/mL of a compound of Formula (I) ortafenoquine which is maintained for at least three weeks after potentialexposure of at least one species of Plasmodium. In further embodiment,administering the compound, or the pharmaceutical composition, achievesa steady state Cmin serum or plasma concentration of at least about 80ng/mL of a compound of Formula (I) or tafenoquine in about greater thanor equal to 50% of malaria naïve, G6PD-normal individuals.

The compounds of the present invention can be administered orally orsublingually. Oral and sublingual dosing can be in a single or divideddose.

The invention also relates to a method of preventing malaria byachieving a steady state Cmin serum or plasma concentration of at leastabout 80 ng/mL of tafenoquine in a malaria naïve, G6PD-normal humansubject. As used herein, “Cmin” refers to the minimum concentration thata drug achieves after the drug has been administered and prior to theadministration of a second or additional dose. Steady state Cmin isachieved when the overall intake of a drug Cmin concentration is fairlyin dynamic equilibrium with its elimination. In some embodiments, Cminconcentration of a compound of Formula (I) or tafenoquine is determinedat one or more points following treatment with techniques known in theart.

EXAMPLES Example 1: Selection of Tafenoquine Doses for MalariaPrevention Utilizing a Pharmacokinetic-Pharmacodynamic Modeling Approach

In a Phase III malaria prophylaxis study in non-immune (the vastmajority of whom were also likely to have been malaria-naïve) Australiansoldiers deployed on peacekeeping duties to Timor-Leste, a weeklyregimen of 200 mg following administration of an initial dose of 200 mgdaily for three days exhibited a protective efficacy of 100% (95%confidence interval [CI] of 93%-100%) (Nasveld P E et al., Randomized,double-blind study of the safety, tolerability, and efficacy oftafenoquine versus mefloquine for malaria prophylaxis in nonimmunesubjects. Antimicrob Agents Chemother. 2010; 54:792-798; Dow G S, McCarthy W F, Reid M, Smith B, Tang D, Shanks D G. A retrospectiveanalysis of the protective efficacy of tafenoquine and mefloquine asprophylactic anti-malarials in non-immune individuals during deploymentto a malaria-endemic area. Malaria Journal. 2014, 13:49). The 200 mgdose selected for the Phase III study was the best tolerated of severaleffective regimens (50, 100, 200 and 400 mg) shown to providestatistically significant reductions in microscopically confirmedparasitemia in Phase II studies in a semi-immune African population(Shanks G D, Oloo A J, Aleman G M, et al. A new primaquine analogue,tafenoquine (WR 238605), for prophylaxis against Plasmodium falciparummalaria. Clin Infect Dis. 2001; 33:1968-1974; Hale B R, Owusu-Agyei S,Fryauff D J, et al. A randomized, double-blind, placebo-controlled,dose-ranging trial of tafenoquine for weekly prophylaxis againstPlasmodium falciparum. Clin Infect Dis. 2003; 36:541-549). A dose of 400mg tafenoquine is generally considered less well tolerated due to ahigher frequency of gastrointestinal adverse events andmethemoglobinemia.

Although the Phase III study in non-immune Australian soldiersdemonstrated that a dose of 200 mg once per day for three days, followedby 200 mg once per week, prevented symptomatic malaria during potentialexposure, the study did not address whether the treatment regimen wouldprevent the development of symptomatic malaria following travel due toexposure late in that period of travel and/or from a latent malarialinfection. Thus, the present modeling study was undertaken to determinea dosing regimen that will provide adequate protection frompost-exposure malarial infection and/or latent malarial infectionthroughout the three week period following exposure, when mostpost-exposure malarial infections or latent malarial infections arise.

Based on the observation in Phase II studies that symptomaticbreakthroughs occurred when plasma tafenoquine concentrations were <40ng/mL, the minimum protective threshold concentration of tafenoquine wasset at 80 ng/mL in the present study (see, e.g., Shanks G D, Oloo A J,Aleman G M, et al. A new primaquine analogue, tafenoquine (WR 238605),for prophylaxis against Plasmodium falciparum malaria. Clin Infect Dis.2001; 33:1968-1974; Hale B R, Owusu-Agyei S, Fryauff D J, et al. Arandomized, double-blind, placebo-controlled, dose-ranging trial oftafenoquine for weekly prophylaxis against Plasmodium falciparum. ClinInfect Dis. 2003; 36:541-549; Llanos-Cuentas A, Lacerda M V,Rueangweerayut R, et al. Tafenoquine plus chloroquine for the treatmentand relapse prevention of Plasmodium vivax malaria (DETECTIVE): amulticentre, double-blind, randomised, phase 2b dose-selection study.Lancet. 2014; 383:1049-1058).

Pharmacokinetic (PK) data from several studies (Phase I/II/III) wasmodeled to establish a consolidated model of tafenoquine and todetermine relevant covariates. More specifically, analysis was performedusing data obtained from ten Phase I/II/III clinical studies oftafenoquine (U.S. Army Study Numbers: 1, 2, 3, 4, 5, 14, 15, 33, 44 and58). Table 2 summarizes the key features of each of the studies includedin the pooled dataset such as the study type and design, dose and dosingregimen, population, and sample collection schemes. A total of 866subjects were included in the population analysis. Ninety-three percentof the subjects were male. A demographic summary pooled across all ofthe available studies is presented in Table 3.

TABLE 2 Clinical Studies of Tafenoquine Study No. N Phase Study TypeStudy Design Doses Population PK Collection 1 45 I Single DoseRandomized, double-blind, TQ 4 to 600 mg or 80 M healthy Before dosingand at 4, 8, 12, Healthy placebo-controlled, placebo volunteers 24, 48,72, 96 and 168 hr after Volunteer Study single oral dose rising (18-35y) dosing. For the six higher dose (fasted) groups (250, 300-600 mg),additional samples were collected on Days 16, 23, 30 and 37. 2 18 ISingle Dose Randomized, TQ 100, 200 or 18 M healthy N/A Healthyparallel-group, single oral 400 mg volunteers Volunteer Study dose(fasted) (18-32 y) 3 4 I Malaria Challenge Randomized, double-blind, TQ600 mg (n = 4) or 4 M/2 F Before dosing and at 5, 7, 12, Study inHealthy placebo-controlled, single placebo (n = 2) volunteers 28 and 42d after dosing on Volunteers dose, fasted, malaria 1 d before (19-30 y)Day 1 challenge sporozoite inoculation 4 25 I Single and RepeatRandomized, double-blind, TQ 200, 400 or 30 M/6 F On Day 1 (Dose 1) andat Dose Healthy placebo-controlled, multiple 600 mg or placebo (23-46 y)Week 10 (Dose 10) before Volunteer Study dose (fasted for ≥ 2 hr) weeklyfor 10 weeks dosing and at 2, 4, 6, 8, 12, 16 and 24 hr after dosing.Additional trough blood samples were drawn pre-dose (weekly) prior toDoses 2 through 9 at Weeks 12, 14, 16, 18 and 20. 5 10 I MalariaChallenge Randomized, double-blind, TQ 600 mg or placebo on 12 M Beforedosing on Day 17, Study in Healthy placebo-controlled, multiple Days −3and −2 before volunteers before dosing on Day 24 and Volunteers oraldose (fed) sporozoite (19-36 y) on Days 26, 31, 38, 45 and 59.inoculation (Day 0), then 300 mg on Days 3, 10, 17 and 24 14 58 IRelative Randomized, relative TQ 400 mg OD for 3 d 43 M/15 F Relative tothe first dose, blood Bioavailability in bioavailability of 3 oral (fed)(21-60 y) samples were collected from Healthy Volunteers formulationseach subject before dosing and up to 96 hr after dosing. Additionalblood samples were collected on an ambulatory basis on Days 6, 7 and 8and in Weeks 4, 6, 8, 10, 12, 14, 16 and 18. 15 34 I Drug-Drug Singlesequence, TQ 400 mg OD for 3 d 20 M/14 F Blood samples for InteractionStudies desipramine interaction (fed); (25-60 y) determination ofSB-252263 in Healthy desipramine 100 mg on (TQ) plasma concentrationsVolunteers morning of Day 1 and were collected up to 96 hr after Day 11(fasted) the second dose of desipramine (Day 11) and thereafter at2-week intervals until 9 weeks after the last (third) dose of SB-252263.33 491 III Malaria Prophylaxis Double-blind, randomized, TQ 200 mg for 3d, then Non-immune During the prophylactic phase Study mefloquine 200 mgweekly Australian (Day 2 and Weeks 4, 8, 16 and positive control MQ 250mg for 3 d, then army troops 26) 250 mg weekly 632 M/22 F (18-51 y) 44135 II Malaria Prophylaxis Double-blind, randomized, TQ 400 mg for 3 d,then Non-immune For the 104 soldiers on Study placebo-controlled 400 mgmonthly Royal Thai monthly TQ prophylaxis, blood Army samples werecollected after 104 M commencing the loading dose randomized to atapproximately 8, 24, 48 and receive TQ and 56 hr and then in intervalsof 101 M 3 ± 4 d until the first monthly randomized to dose. After eachmonthly dose, receive placebo samples were collected at approximately 8hr after dosing, mid-month and at the end of the monthly dose (troughplasma drug concentration). Following the last monthly dose, sampleswere collected at approximately 4, 8, 12 and 24 hr and then in intervalsof 3 ± 4 d for 2 months. At each blood collection, samples were obtainedfrom 2 to 28 volunteers (mean ± SD, 12.6 ± 7.1 volunteers). For the 31soldiers on weekly prophylaxis, blood samples were collected after 2 ±22 weeks of medication (mean ± SD, 11.8 ± 6.8 weeks). Samples from thisgroup were collected at approximately 12 hr and 168 hr after weeklymedication and at 14, 21 and 28 d after the last dose. 58 46 II P. vivaxTreatment Randomized, TQ 400 mg OD for 3 d in 120 M/F Daily for Days0-7, Days 12-20 Study active-control, Cohort 1 and TQ 600 mg (60 in eachand Days 28-30 double-blind, OD for 1 d in Cohort 2 cohort) double-dummy(20-60 y) d: days; F: female; hr: hours; M: male; MQ: mefloquine; N:number of subjects; N/A: not available; No.: number; OD: once daily; PK:pharmacokinetic; SD: standard deviation; TQ: tafenoquine; y: years.

TABLE 3 Demographic Summary of Subjects in the Tafenoquine Population PKAnalysis Baseline Characteristic Statistic All Subjects Male FemaleNumber of subjects n (%) 866 808 (93.3) 58 (6.7) Age (years) Mean 27.827.1 37.2 SE 0.28 0.25 1.68 Median 25.0 25.0 35.0 Min, Max 18.0, 60.0 18.0, 60.0  19.0, 60.0 Race Asian n (%) 181 (20.9) 172 (19.9)  9 (1.0)Black or African n (%) 26 (3.0) 21 (2.4)  5 (0.6) Caucasian/White n (%)626 (72.3) 582 (67.2) 44 (5.1) Hispanic n (%) 31 (3.6) 31 (3.6) — Othern (%)  2 (0.2)  2 (0.2) — Food No n (%)  92 (10.6) 86 (9.9)  6 (0.7) Yesn (%) 774 (89.4) 722 (83.4) 52 (6.0) Weight (kg) Mean 75.0 75.9 62.4 SE0.47 0.48 1.37 Median 75.0 76.0 62.3 Min, Max 43.0, 135.0 43.0, 135.043.0, 88.0 n: number of subjects; Min: minimum; Max: maximum; PK:pharmacokinetic; SE: standard error.

To summarize the conclusions of this analysis, this analysisdemonstrated that a dosing regimen involving an initial dose of 200 mgonce per day for three days followed by exposure doses of 200 mg weekthroughout the period of exposure would result in trough plasmatafenoquine concentrations >80 ng/mL in >95% of individuals. Severalalternative dosing regimens that incorporated removal of the initialdose, lowering of the dose given, and monthly administration were alsomodeled to determine whether they would achieve troughconcentrations >80 ng/mL in >50% of individuals. We also modeled twopost-exposure prophylaxis regimens to assess the duration of time inwhich protective plasma tafenoquine concentrations could be maintained.Our results show that an initial dose of 200 mg daily for three daysfollowed by weekly 200 mg exposure doses continued as post-exposuredoses until three weeks after potential exposure (e.g., deployment to amalaria area) should offer protection against malaria both throughoutthe period of exposure and for the period after exposure when latentmalarial infections can arise (e.g., three weeks post-exposure).

Methods:

The tafenoquine concentrations of plasma samples across the ten studieswere analyzed using a validated high-performance liquidchromatography-mass spectrometry method (HPLC-MS) or HPLC withfluorescence detection as previously described (see, Kocisko D A, WalshD S, Eamsila C, Edstein M D. Measurement of tafenoquine (WR 238605) inhuman plasma, and venous and capillary blood by high-pressure liquidchromatography. Ther Drug Monit. 2000; 22:184-189; Charles B G, Miller AK, Nasveld P E, Reid M G, Harris I E, Edstein M D. Populationpharmacokinetics of tafenoquine during malaria prophylaxis in healthysubjects. Antimicrob Agents Chemother. 2007; 51:2709-2715.

Population PK analyses were carried out using NONMEM version 7.1.2,PDx-Pop version 4.2 (Icon Development Solutions, Hanover, Md.) and IntelVisual Fortran Compiler version 12 on a Microsoft Windows XP platform.Plasma tafenoquine concentrations, demographic information and clinicallaboratory results from ten studies were used to build a pooled NONMEMinput data file for the current population PK analysis. The data wereprepared for analysis using SAS software version 9.1.3 (SAS InstituteInc., Cary, N.C.). Actual dosing and actual blood sampling times, whenavailable, were used for the analysis. Plasma tafenoquine concentrationsthat were below or equal to the limit of quantification were excludedfrom the analysis.

Based on the PK profile of tafenoquine from previous modeling efforts(Shanks G D, Oloo A J, Aleman G M, et al. A new primaquine analogue,tafenoquine (WR 238605), for prophylaxis against Plasmodium falciparummalaria. Clin Infect Dis. 2001; 33:1968-1974; Obaldia N 3rd, Rossan R N,Cooper R D, et al. WR 238605, chloroquine, and their combinations asblood schizonticides against a chloroquine-resistant strain ofPlasmodium vivax in Aotus monkeys. Am J Trop Med Hyg. 1997; 56:508-10),a one-compartment PK model with first-order absorption and eliminationprocesses was selected to describe best the pharmacokinetics oftafenoquine. As part of the modeling process, a two-compartment PK modelwith first-order absorption and elimination process was also exploredand discarded. The one-compartment PK model was specified in the NONMEMcontrol file and was parameterized in terms of apparent clearance(CL/F), apparent volume of distribution (V/F) and absorption rateconstant (Ka) using the PREDPP ADVAN2 with TRANS2 subroutine in NONMEM.First-order conditional estimation (FOCE) with interaction betweenvariance of inter-individual variability and the variance of residualerror was used as the estimation method. Inter-individual variabilitywas best described by an exponential error model, as shown below:Pi={circumflex over (P)}exp(η_(i))

-   -   where:    -   Pi is the estimated parameter for the i^(th) individual.    -   {circumflex over (P)} is the population value for the parameter.    -   η_(i) are inter-individual random effects for the i^(th)        individual for parameter P and were assumed to be independent        and symmetrically distributed with a zero mean and a variance        ω².

Different structural models (additive, proportional, exponential andcombined additive and proportional) were investigated for residualunexplained variability (RUV). RUV was best described by a proportionalerror model, as shown below:C _(ij) =Ĉ _(ij)(1+ε_(pij))

-   -   where:    -   C_(ij) is the j^(th) observation for the i^(th) individual.    -   Ĉ_(ij) is the j^(th) predicted value for the i^(th) individual.    -   ε_(pij) is the proportional residual random error for the i^(th)        individual and the j^(th) measurement and was assumed to be        independent and symmetrically distributed with a zero mean and a        variance σ².

For optimal model selection, diagnostic plots were generated by PDx-Popversion 4.2 in conjunction with Microsoft Excel and S+ version 8. Thestandard criteria of change in the minimum objective function value(ΔOFV) equal to minus twice the log-likelihood of the data as well asdiagnostics were used to assess goodness of fit. Successful model runswere determined by each of the following criteria: successful modelconvergence; a minimum of three significant figures reported for anyparameter; a non-singular covariance matrix; completion of thecovariance step without warnings; CIs for the structural parameters thatdid not include zero; absence of trends in the distribution of weightedresiduals versus model predictions and in the weighted residuals versusthe independent variable; and insensitivity of model convergence andcovariance to initial parameter estimates.

Covariate analysis was performed to the base PK model to identify and toevaluate the extent to which the covariates accounted for thevariability in the PK parameters. Prior to including covariates in thepopulation model, visual inspection of the relationship between each ηand covariate was performed using scatter plots. The scatter plots werealso used to provide visual identification of collinearity between thecovariates of interest. Covariates that were identified to demonstratecollinearity based on exploratory plots were not allowed to enter thecovariate model at the same time. The decision to include covariates inthe final model was also based on whether it was sensiblephysiologically to include them.

Sex, age, race and body weight (WT) were selected for evaluation aspotential covariates of CL/F, V/F and Ka. Starting with the base PKmodel, a process was initiated in which covariates were selected one ata time and included in the model if inclusion resulted in a reduction inthe OFV of at least 3.84 (p 0.05, df=1). This process was followed by amultivariate analysis, in which all selected covariates were addedtogether and the model was fit to the data, resulting in the full PKmodel. Backward deletion was applied by dropping one covariate at a timeuntil no covariate could be removed without significantly increasing theOFV (p≤0.001), resulting in the final PK model. However, if a CI of anyof the covariate effects included the null value, the effect wasconsidered not significant and the model was further simplified untilall structural parameters were well estimated. Continuous covariates inthe model were centered on the population median value of the subjectsincluded in the analysis and are described in more detail in the resultssection.

The final PK model was evaluated using bootstrapping and a visualpredictive check. Using the bootstrap approach, the bootstrap parametervalues were obtained by repeatedly fitting the final population model to1000 bootstrap samples. The mean and CI values of the bootstrapparameters were then compared to the final population model parameterestimates and associated CIs from NONMEM. The 95% bootstrap percentileCIs were determined for the PK parameters derived from 1000 bootstrapdatasets and compared to the original parameters obtained from the finalmodel.

A visual predictive check was performed by simulating the plasmatafenoquine concentrations from the original subjects in the NONMEMdataset using the parameter estimates from the final PK model. Onethousand predicted profiles were simulated for each original subject.Random effects were included in the simulation. The median, 5^(th)percentile and 95^(th) percentile PK concentration-versus-time profilesfrom the simulations were compared with those from observed plasmatafenoquine concentrations.

Simulations of PK data for various doses and dose regimens wereperformed using the final PK model parameters. The simulation stepincluded creation of NONMEM data files with virtual subjects withdesired sampling times and dosing regimens and running of thesimulations with 2000 replicates using the final PK model parameters inNONMEM. The outputs from the simulations were summarized using SASsoftware version 9.1.3 and presented graphically using Phoenix WinNonlinversion 6.2 (Pharsight, St. Louis, Mo.).

A one-compartment PK model with first-order absorption and eliminationrate constants was selected as the structural model. Different errormodels for inter-individual and residual unexplained variability werealso tested. The exponential error model was chosen to describeinter-individual variability of each PK parameter (CL/F, V/F and Ka) andthe proportional error model was chosen to describe residual error. Atwo-compartment PK model was also tested but was not pursued furtherbecause of unreliable estimates from bootstrap results during modelevaluation (data not shown).

Because age, WT, race, sex and meal condition (fed versus fasted) werethe only common covariates present for all ten studies, these covariateswere selected for covariate model exploration. Each of these covariateswas included in the base PK model to test for its significance. Becausediversity in race was restricted due to a majority of the subjects beingAsian or Caucasian, the effect of race was explored only for Asiansubjects versus Caucasian/other subjects as the reference. Sex and racewere confounded with WT and were not explored further in the fullcovariate model.

The full covariate model included the effect of WT on CL/F and V/F; ageon CL/F, V/F and Ka; and meal condition on V/F and Ka. The effect ofmeal condition on bioavailability alone could not be explored and theeffect of meal condition on CL/F was not significant. The full covariatePK model was further reduced by backward elimination and resulted in WTand age as significant covariates of CL/F, and WT and meal condition assignificant covariates of V/F. Goodness-of-fit plots are presented inFIG. 1 and support that the model fit available concentration data.

Base structural parameters and the relationship of covariates to CL/Fand V/F are summarized in Table 4. For oral tafenoquine, the populationCL/F and V/F were determined to be 4.17 L/h and 2470 L, respectively.The first-order Ka of oral tafenoquine was 0.359 The inter-individualvariability of CL/F, V/F and Ka was 23.6%, 24.1% and 54.1%,respectively. The final PK model revealed that CL/F of tafenoquine is afunction of WT and age. These covariates decreased inter-individualvariability associated with CL/F from 26.5% to 23.6%. The relationshipbetween CL/F and both covariates was as follows:CL/F (L/h)=4.17×(WT/75)^(0.552)×(AGE/25)^(−0.2)

TABLE 4 Tafenoquine Population PK Parameters of the Final PK ModelParameters Bootstrap 95% CI Inter-individual (Units) Final EstimateLower Upper Variability a CL/F (L/h) = θ_(CL) × (WT/75)^(θ) ^(CL-WT) ×(AGE/25)^(θ) ^(CL-AGE) θ_(CL) 4.17 4.080 4.230 23.6% θ_(CL-WT) 0.5520.474 0.637 θ_(CL-AGE) −0.200 −0.267 −0.138 V/F (L) = θ_(V) ×(WT/75)^(θ) ^(V-WT) × (θ_(V-FOOD))^(FOOD) θ_(V) 2470 2340 2630 24.1%θ_(V-WT) 0.781 0.652 0.901 θ_(V-FOOD) 0.822 0.761 0.861 Ka (1/h) 0.3590.321 0.384 54.1% ω² _(CL) 0.0555 0.0462 0.0618 COV_(CL, V) 0.02890.0186 0.0315 ω² _(V) 0.0583 0.0444 0.0606 ω² _(Ka) 0.293 0.203 0.378 σ²0.0488 0.0436 0.0553 CL or CL/F: apparent clearance; CI: confidenceinterval; COV: covariance; hr: hours; Ka: absorption rate constant; PK:pharmacokinetic; V or V/F: apparent volume of distribution; WT: weight;ω²: variance of the inter-individual random effect; σ²: variance of theproportional residual random effect. a The magnitude of inter-individualvariability was presented as the coefficient of variation. Note: Finalestimate and inter-individual variability were from NONMEM estimates.FOOD = 0 for fasted and 1 for fed.

Thus, tafenoquine CL/F was found to increase as WT increased (expressedin kilograms) and to decrease with age (expressed in years).

The final PK model revealed that V/F of tafenoquine is a function of WTand meal condition. These covariates decreased the inter-individualvariability of V/F from 29.6% to 24.1%. The relationship between V/F andboth covariates was as follows:V/F (L)=2470×(WT/75)^(0.781)×(0.822)^(FOOD)where FOOD=0 for fasted and 1 for fed.

Tafenoquine V/F was found to increase as WT increased and to decrease inthe fed condition compared with the fasting condition.

The bootstrapping technique was used to evaluate the final PK model. Thecomparison between the parameter estimates derived from the bootstrapand the estimates derived from NONMEM and between the estimates of thevariability of the random effects derived from the bootstrap and thecorresponding NONMEM estimates are presented in Table 5. In thismodeling effort, the differences of mean bootstrap estimates from theNONMEM estimates of those parameters were less than 15%. Overall, themean population PK parameter estimates and 95% CI obtained from thebootstrap procedure were comparable to the estimates and 95% CI from thefinal PK model. The success rate of bootstrap runs was 100% for the PKmodel.

TABLE 5 Comparison of Bootstrap and NONMEM Parameter Estimates forTafenoquine Parameters NONMEM Estimate Bootstrap Estimate Difference^(a) θ_(CL) 4.17 4.15 −0.37% θ_(CL-WT) 0.552 0.554 0.35% θ_(CL-AGE)−0.200 −0.200 0.08% θ_(V) 2470 2482 0.47% θ_(V-WT) 0.781 0.774 −0.96%θ_(V-FOOD) 0.822 0.810 −1.52% θ_(KA) 0.359 0.351 −2.29% ω² _(CL) 0.05550.0536 −3.44% COV_(CL, V) 0.0289 0.0250 −13.40% ω² _(V) 0.0583 0.0521−10.55% ω² _(Ka) 0.293 0.283 −3.49% σ² 0.0488 0.0486 −0.50% CL or CL/F:apparent clearance; COV: covariance; Ka: absorption rate constant; PK:pharmacokinetic; V or V/F: apparent volume of distribution; WT: weight;ω²: variance of the inter-individual random effect; σ²: variance of theproportional residual random effect. ^(a) Expressed as percent ofdifference between bootstrap and NONMEM estimates from the final model([Bootstrap/NONMEM − 1] × 100%).

The visual predictive check was performed using the NONMEM parameterestimates estimated from the final PK model. Median, 5^(th) percentileand 95^(th) percentile plots of model-predicted versus observed plasmatafenoquine concentrations are presented in FIG. 2. The resultsdemonstrate the adequacy of the final PK model to reproduce a majorityof plasma tafenoquine concentrations over the course of several doselevels. 90.56% of the observations were within the 90% predictioninterval (4.90% were below the 5^(th) percentile and 4.55% were higherthan the 95^(th) percentile).

Results:

The simulated reference regimen (200 mg daily for three days then 200 mgweekly) resulted in the achievement of plasma tafenoquineconcentrations >80 ng/mL immediately after the loading dose in 95% ofindividuals (FIG. 3). Concentrations decreased below this thresholdbriefly in more than 5% of Australian soldiers at the first trough butremained above 80 ng/mL throughout the remainder of the simulatedsix-month deployment in 95% of individuals (FIG. 3). Median tafenoquinesteady-state trough plasma concentrations after simulation of thereference regimen decreased as WT increased but were predicted to remainhigher than the desired threshold in the majority of individuals at alllevels of body weight (FIG. 4). After administration of the referenceregimen in the fed meal condition, plasma tafenoquine concentrationswere increased prior to the attainment of steady-state; however, thisincrease was expected to have a minimal impact on plasma tafenoquineconcentrations at steady-state (FIG. 4). Plasma tafenoquineconcentrations at steady-state following the administration of thereference regimen were expected to increase with an increase in age(FIG. 5), and this increased concentration was most likely due to theeffect of age on CL/F. However, steady state concentrations were higherin the majority of individuals at all ages.

Variations of the Reference Regimen are simulated in FIG. 7. Insimulations in which the initial dose component of the intended regimenwas removed (Compare Regimen 1), and/or or the dose was lowered to 100or 150 mg (Regimens 2 and 6) median trough plasma tafenoquineconcentrations exceeded the intended 80 ng/mL after two or three weeklydoses. Simulation of the prophylactic monthly regimen utilized in Thaimarines (Regimen 4, FIG. 7) predicted that median steady-state troughplasma tafenoquine concentrations >80 ng/mL did not persist for theentire simulated deployment (FIG. 7) and were lower than those of theReference Regimen, and Regimens 1, 2 and 6 (compare FIGS. 3 and 7). Inthe simulation in which 50 mg was given weekly with no loading dose(Regimen 7), median steady state trough concentrations never exceededthe intended threshold.

Upon return from a malaria endemic area, it is usual practice toadminister a regimen for post-exposure prophylaxis to reduce the risk ofcontracting P. falciparum malaria in the final three weeks of deploymentand to prevent P. vivax relapses. Simulation of the administration of apost-exposure prophylaxis regimen of 200 mg once daily for three days(Regimen 3, FIG. 7) or 200 mg once weekly for three weeks (extendedReference Regimen, FIG. 8) predicted that plasma tafenoquineconcentrations >80 ng/mL will be maintained for greater than one month(FIGS. 7 and 8). In addition, the peak plasma concentration (Cmax) oftafenoquine after administration of Regimen 3 (i.e., following a reverseload of 200 mg daily for three days) was predicted to be lower than thatattained after administration of the loading dose of 400 mg daily forthree days employed both in Thai marines (Llanos-Cuentas A, Lacerda M V,Rueangweerayut R, et al. Tafenoquine plus chloroquine for the treatmentand relapse prevention of Plasmodium vivax malaria (DETECTIVE): amulticentre, double-blind, randomised, phase 2b dose-selection study.Lancet. 2014; 383:1049-1058) and in semi-immune residents of Kenya (LiQ, O'Neil M, Xie L, et al. Assessment of the prophylactic activity andpharmacokinetic profile of oral tafenoquine compared to primaquine forinhibition of liver stage malaria infections. Malar J. 2014; 13:141)(Regimen 4, FIG. 7), see FIG. 7 for full profile and compare FIGS. 3 and8 for concentrations after the last dose).

A total of 866 subjects were included in this population PK modeling oftafenoquine. Results showed that a one-compartment PK model withfirst-order absorption and elimination was an appropriate base PK modelfor describing the pharmacokinetics of tafenoquine administered orally.Inter-individual variability was described by an exponential model andresidual variability was described by a proportional model. Modelevaluation using bootstrapping and the visual predictive check confirmedthe reliability of the final PK model and its reproduction of plasmatafenoquine concentrations.

Variability in the final PK model was explained by the effect of changesin WT and age on CL/F, and WT and meal status on V/F although assessmentof the effect of meal status on V/F was limited by the relatively smallpercentage of subjects dosed under fasted conditions. The explainedvariability is not sufficient to suggest that the intended regimenshould be modified based on either age or meal status in order toachieve the desired steady-state plasma tafenoquine concentration,because the reference regimen is predicted to result in the attainmentof the intended steady-state trough plasma tafenoquine concentrationsin >95% of individuals. The effect of WT, age and meal status areevident, but even in these sub-populations, protective plasmatafenoquine concentrations are achieved in the vast majority ofindividuals.

The data shows that removal of the loading dose and/or lowering the doseto 100 or 150 mg would result in the attainment of protective plasmatafenoquine concentrations over the entirety of the simulated deploymentof six months. Protective concentrations would be reached with all theseregimens after the second or third dose. A monthly dosing schedule ispredicted not to result in the attainment of protective plasmatafenoquine concentrations over the entirety of the simulated deploymentof six months, confirming clinical experience with this regimen in Thaimarines (Edstein M D, Kocisko D A, Walsh D S, Eamsila C, Charles B G,Rieckmann K H. Plasma concentrations of tafenoquine, a new long-actingantimalarial agent, in Thai soldiers receiving monthly prophylaxis. ClinInfect Dis. 2003; 37:1654-1658).

As highlighted in a recent retrospective analysis of the efficacy oftafenoquine in non-immune subjects (Dow G S, Mc Carthy W F, Reid M,Smith B, Tang D, Shanks D G. A retrospective analysis of the protectiveefficacy of tafenoquine and mefloquine as prophylactic anti-malarials innon-immune individuals during deployment to a malaria-endemic area.Malaria Journal. 2014, 13:49), a post-dosing regimen may be needed tomanage the residual risk of malaria from later exposure during travel.We explored two post-exposure prophylaxis regimens of tafenoquine:administration of a reverse load of 200 mg once daily for three days(Regimen 3) versus extension of the reference regimen for an additionalthree weeks. The extended reference regimen maintained trough plasmatafenoquine concentrations >80 ng/mL for approximately three to fourdays longer in 95% of individuals than did the reverse load, buttafenoquine concentrations of both regimens remained in excess of thethreshold in a majority of individuals for at least one month. The Cmaxof tafenoquine achieved after administration of the reverse load waslower than that attained after administration of 400 mg once daily forthree days. A loading dose of 400 mg once daily for three days has beenshown to be safe in G6PD-normal individuals in several clinical studiesbut exhibits gastrointestinal intolerability (Shanks G D, Oloo A J,Aleman G M, et al. A new primaquine analogue, tafenoquine (WR 238605),for prophylaxis against Plasmodium falciparum malaria. Clin Infect Dis.2001; 33:1968-1974; Walsh D S, Eamsila C, Sasiprapha T, et al. Efficacyof monthly tafenoquine for prophylaxis of Plasmodium vivax andmultidrug-resistant P. falciparum malaria. J Infect Dis. 2004;190:1456-1463; Elmes N J, Nasveld P E, Kitchener S J, Kocisko D A,Edstein M D. The efficacy and tolerability of three different regimensof tafenoquine versus primaquine for post-exposure prophylaxis ofPlasmodium vivax malaria in the Southwest Pacific. Trans R Soc Trop MedHyg. 2008; 102:1095-1101). The incidence of gastrointestinal adverseevents after the administration of 200 mg tafenoquine once daily forthree days (total dose 600 mg) is approximately half of that afteradministration of 400 mg once daily or BID for three days (total dose1200 mg) and similar to the standard of care (Elmes N J, Nasveld P E,Kitchener S J, Kocisko D A, Edstein M D. The efficacy and tolerabilityof three different regimens of tafenoquine versus primaquine forpost-exposure prophylaxis of Plasmodium vivax malaria in the SouthwestPacific. Trans R Soc Trop Med Hyg. 2008; 102:1095-1101). It is thereforeconceivable that gastrointestinal intolerability might be no worse thanthe standard of care for those who receive the reverse load (200 mg oncedaily for three days). However, additional clinical data are required todemonstrate this directly.

Recent reports have associated P. vivax relapses/primaquine failureswith polymorphisms in cytochrome P450 (CYP) 2D6 (Bennett J W, Pybus B S,Yadava A, et al. Primaquine failure and cytochrome P-450 2D6 inPlasmodium vivax malaria. N Engl J Med. 2013; 369:1381-1382).Presumably, this is because the production of an unknown primaquinemetabolite that is important for P. vivax anti-hypnozoite activity isinhibited in individuals with CYP2D6 mutations. Conceivably, the samemight also be true for tafenoquine. If so, it likely has no clinicalrelevance in the context of prophylactic use. This is because at thereference regimen described here, no malaria breakthroughs were observedin a large cohort of non-immune and primarily Caucasian Australiansoldiers (Bennett J W, Pybus B S, Yadava A, et al. Primaquine failureand cytochrome P-450 2D6 in Plasmodium vivax malaria. N Engl J Med.2013; 369:1381-1382). Although CPY2D6 polymorphisms were not determinedin the 491 Australian soldiers who received tafenoquine, a good numberwould have been poor metabolizers, because the prevalence of CYP2D6 poormetabolizers in Caucasian populations ranges from 6% to 10% (AustralianMedicines Handbook 2004. Adelaide: Australian Medicines Handbook PtyLtd; 2004).

The Australian and U.S. Armed Forces routinely use daily doxycycline oratovaquone/proguanil for malaria prophylaxis (DOD Health Memo:http://www.health.mil/˜/media/MHS/Policy%20Files/Import/13-002.ashx;Shanks G D, Elmes N J. Malaria in the military and Melanesia. ADFHealth, 2008; 9:54-59). Weekly mefloquine is used where the risk-benefitis appropriate (DOD Health Memo:http://www.health.mil/˜/media/MHS/Policy%20Files/Import/13-002.ashx).Post-exposure prophylaxis usually involves administration of ablood-schizonticidal anti-malarial for one month (doxycycline ormefloquine), a causal prophylactic drug for seven days(atovaquone/proguanil) and/or a combination of a blood-schizonticidaldrug (doxycycline) and primaquine for two weeks to reduce the risk of P.vivax relapse or the contraction of P. falciparum malaria fromlate-deployment exposure (DOD Health Memo:http://www.health.mil/˜/media/MHS/Policy%20Files/Import/13-002.ashx;Shanks G D, Elmes N J. Malaria in the military and Melanesia. ADFHealth. 2008; 9:54-59). Weekly tafenoquine extended for three weeksfollowing deployment is predicted to maintain the same level ofprotection as the standard of care and provide a more convenientprophylaxis and post-exposure prophylaxis regimen. Compression of thepost-exposure prophylactic regimen to a three-day reverse load (200mg/day or lower daily dose for 3 days) could further economize thedosing schedule, and thus improve compliance, but additional clinicaldata are required to assess GI tolerability. There will remain a smallrisk of P. vivax relapses, but this risk is not anticipated to begreater than that of the standard of care (blood schizontocide plusprimaquine 30 mg/day for 14 days) (Elmes N J, Nasveld P E, Kitchener SJ, Kocisko D A, Edstein M D. The efficacy and tolerability of threedifferent regimens of tafenoquine versus primaquine for post-exposureprophylaxis of Plasmodium vivax malaria in the Southwest Pacific. TransR Soc Trop Med Hyg. 2008; 102:1095-1101).

In Example 1, the population pharmacokinetics of tafenoquine wereassessed using data from ten Phase I/II/III clinical studies, resultingin a stable, predictive model used to confirm the efficacy of theintended reference tafenoquine regimen (200 mg/day for 3 days, then 200mg weekly) and to explore additional regimens. Elimination of theloading dose and/or reduction of the dose to 100 and 150 mg maintainedprotective levels of drug in the majority of individuals. Two additionalpost-exposure prophylaxis regimens (Regimen 3 reverse load of 200 mg/dayfor 3 days and the extended reference regimen) showed promise for beingwell tolerated and effective. Tafenoquine administered weekly for threeweeks following deployment is predicted to maintain the same level ofprotection as the standard of care and provide a more convenientprophylaxis and post-exposure prophylaxis regimen. Compression of thepost-exposure prophylactic regimen to a three-day reverse load (Regimen3) could further economize the dosing schedule. A small risk of P. vivaxrelapse will remain but is not anticipated to be greater than that ofthe standard of care.

REFERENCES

-   1. Brueckner R P, Coster T, Wesche D L, Shmuklarsky M, Schuster B G.    Prophylaxis of Plasmodium falciparum infection in a human challenge    model with WR 238605, a new 8-aminoquinoline antimalarial.    Antimicrob Agents Chemother. 1998; 42:1293-1294.-   2. Marcsisin S R, Sousa J C, Reichard G A, et al. Tafenoquine and    NPC-1161B require CYP 2D metabolism for anti-malarial activity:    implications for the 8-aminoquinoline class of anti-malarial    compounds. Malar J 2014; 13:2.-   3. Idowu O R, Peggins J O, Brewer T G, Kelley C. Metabolism of a    candidate 8-aminoquinoline antimalarial agent, WR 238605, by rat    liver microsomes. Drug Metab Dispos. 1995; 23:1-17.-   4. Lobel H O, Bernard K W, Williams S L, Hightower A W, Patchen L C,    Campbell C C. Effectiveness and tolerance of long-term malaria    prophylaxis with mefloquine. Need for a better dosing regimen. JAMA.    1991; 26:361-364.-   5. Lobel H O, Miani M, Eng T, Bernard K W, Hightower A W, Campbell    C C. Long-term malaria prophylaxis with weekly mefloquine. Lancet.    1993; 341:848-851.-   6. Food and Drug Administration Guidance for Industry.    Exposure-Response Relationships—Study Design, Data Analysis, and    Regulatory Applications. 2003.

The teachings of all patents, published applications, and referencescited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method of prevention of symptomatic P.falciparum malaria in a human subject, comprising: a) administering tothe human subject two or more initial doses of a compound of Formula(I), a pharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I) over a period of 1-7days, wherein at least the first initial dose is administered prior topotential exposure of the subject to P. falciparum; and b) administeringto the human subject an exposure dose of said compound or compositionone or more times per week during potential exposure of the subject toP. falciparum, wherein about 100 mg to about 275 mg of said compound ofFormula (I) is administered in each of said two or more initial doses,wherein the total combined amount of said compound of Formula (I)administered in said initial doses is about 500 mg to about 900 mg,wherein the total amount of said compound of Formula (I) administeredthrough said exposure dose(s) is about 100 mg to about 275 mg per week,wherein the administration is sufficient to produce a Cmin serum orplasma concentration of at least about 80 ng/mL of said compound ofFormula (I) prior to potential exposure to P. falciparum and tosubstantially maintain that serum or plasma concentration throughout toP. falciparum in more than 50% of individuals administered the giveninitial and exposure doses, wherein the human subject is malaria-naveand Glucose-6-phosphate dehydrogenase (G6PD) normal, and wherein Formula(I) has the following structure,


2. The method of claim 1, wherein the amount of the compound of Formula(I) administered in each of said two or more initial doses is about 200mg and said initial doses are administered once per day for three days,and wherein the total amount of the compound of Formula (I) administeredthrough the exposure dose is about 200 mg once per week.
 3. The methodof claim 1, wherein the exposure dose is a daily dose of 25 mg.
 4. Themethod of claim 1, wherein the initial doses are administered once perday for three days.
 5. The method of claim 4, wherein the amount of thecompound of Formula (I) administered in each of said initial doses isabout 200 mg.
 6. The method of claim 1, wherein the total amount of thecompound of Formula (I) administered in the exposure dose(s) is about200 mg per week.
 7. The method of claim 1, wherein the exposure dose(s)are administered once per week.
 8. The method of claim 1, wherein theinitial dose is about 165 mg, about 180 mg, about 210 mg, about 240 mg,or about 270 mg of the compound of Formula (I) administered once per dayfor three days, and wherein the total administered amount of theexposure dose is about 100 mg per week, 150 mg per week, about 165 mgper week, about 180 mg per week, about 210 mg per week, or about 270 mgper week of the compound of Formula (I).
 9. The method of claim 1,wherein the exposure dose is a daily dose of about 30 mg of the compoundof Formula (I).
 10. The method of claim 1, wherein the initial dose isadministered three times.
 11. The method of claim 1, wherein theexposure dose is administered once per day.
 12. The method of claim 1,wherein the subject has low body weight or age, wherein the amount ofthe compound of Formula (I) in each of said two or more initial dosescomprises about 1-5 mg/kg of body weight each day, and wherein the totalweekly amount of the compound of Formula (I) in the exposure dose(s)comprises about 1-5 mg/kg of body weight each week.
 13. The method ofclaim 1, wherein the combined total amount of the compound of Formula(I) administered in the two or more initial doses does not exceed about600 mg, and the total amount of the compound of Formula (I) administeredin the exposure doses does not exceed about 270 mg per week.
 14. Themethod of claim 13, wherein the initial dose is about 80-100 mg of thecompound of Formula (I) administered once per day for six days, and theexposure dose is about 20 mg, about 25 mg, about 30 mg, about 35 mg, orabout 40 mg of the compound of Formula (I) administered once per day.15. The method of claim 1, wherein the administration is sufficient toproduce a Cmin serum or plasma concentration of at least about 80 ng/mLof the compound of Formula (I) prior to potential exposure to P.falciparum and to substantially maintain that serum or plasmaconcentration throughout potential exposure to P. falciparum in 95% ormore of a population of subjects administered the given initial andexposure doses.
 16. The method of claim 1, wherein the human subject isan adult.
 17. The method of claim 1, wherein the human subject is achild.
 18. The method of claim 1, wherein the compound, the salt, or thepharmaceutical composition is administered orally or sublingually. 19.The method of claim 1, wherein the total combined amount of the compoundof Formula (I) administered in said two or more initial doses is about525-585 mg.
 20. A kit comprising: a) two or more initial dose(s) ofabout 100 to about 270 mg of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I); b) a plurality ofexposure doses of the compound, salt, or composition, wherein the totalamount of the exposure dose to be administered is about 100 to about 275mg per week of the compound of Formula (I); and c) instructions fortaking said two or more initial doses, wherein at least the firstinitial dose is taken prior to potential exposure of the subject to P.falciparum, and for taking said exposure doses one or more times perweek during potential exposure of the subject to P. falciparum, whereinFormula (I) has the following structure,


21. The method of claim 1, wherein the pharmaceutically acceptable saltof a compound of Formula (I) is tafenoquine succinate.
 22. The method ofclaim 1, wherein the pharmaceutically acceptable salt of a compound ofFormula (I) is a salt of tafenoquine or a salt having the followingstructure,


23. The method of claim 1, wherein the exposure dose is administered oneto seven times per week.
 24. The method of claim 1, wherein each of thetwo or more initial doses is about 150 mg of the compound of Formula(I), wherein the initial doses are administered four times, and whereinthe exposure doses are about 150 mg administered weekly.
 25. The methodof claim 1 further comprising administering to the human subject one ofmore post-exposure dose(s) of a compound of Formula (I), apharmaceutically acceptable salt thereof, or a pharmaceuticalcomposition comprising a compound of Formula (I), within 1-10 days afterthe risk of continued exposure to P. falciparum has substantially ended,wherein each said post-exposure dose comprises 150 mg to about 300 mg ofthe compound of Formula (I).
 26. The method of claim 25, wherein thepost-exposure dose is about 150 mg of the compound of Formula (I) and isadministered once.
 27. The method of claim 25, wherein the post-exposuredose is about 200 mg of the compound of Formula (I) and is administeredonce.
 28. The method of claim 25, wherein the total combinedpost-exposure dose is about 300 mg of the compound of Formula (I) thatis administered in one to three separate post-exposure doses.
 29. Themethod of claim 25, wherein the total combined post-exposure dose isabout 300 mg of the compound of Formula (I) that is administered in twoseparate post-exposure doses.
 30. The method of claim 25, wherein eachof the two or more initial doses is about 200 mg of the compound ofFormula (I), wherein the initial doses are administered once per day forthree days prior to potential exposure, wherein the exposure dose isabout 200 mg of the compound of Formula (I) administered once per weekduring potential exposure, and wherein the post-exposure dose is about200 mg of the compound of Formula (I) administered once.
 31. The methodof claim 1, wherein a Cmin serum or plasma concentration of at leastabout 80 ng/mL of the compound of Formula (I) is obtained prior topotential exposure to P. falciparum and is substantially maintainedthroughout potential exposure to P. falciparum in the human subject.